From small clandestine offices in countries as far flung as Qatar, Jordan, Turkey and Croatia, US Central Intelligence Agency (CIA) officers have acted as brokers and overseers of a massive arms shipment programme to Syria's opposition rebels.
With the operation shrouded in secrecy, the CIA declines to comment publicly on the arms supply. US officials instead talk of its existence in a kind of coded doublespeak referring to "a maturing of the opposition's logistical pipeline."
But exist it definitely does, and according to arms-trafficking investigators who are monitoring data on the weapons' supplies, the scale of the shipments is huge.
"A conservative estimate of the payload of these flights would be 3500 tons of military equipment," confirmed Hugh Griffiths, of the Stockholm International Peace Research Institute, in a recent detailed analysis of the illicit transfer outlined in a New York Times (NYT) investigation.
"The intensity and frequency of these flights," says Griffiths, are "suggestive of a well-planned and co-ordinated clandestine military logistics operation."
According to the data compiled and information gleaned from Syrian rebel commanders, the NYT investigation reveals that, with CIA help, both Qatar and Saudi Arabia have been moving military material via Esenboga airport in Turkey to the opposition since, respectively, early and late 2012.
Towards the end of last year it appears a major obstacle to this process was removed after the Turkish government agreed to a rapid increase in the supply chain.
Evidence in the NYT report also points to arms and equipment being bought by Saudi Arabia in Croatia and flown to Jordan on Jordanian cargo planes for rebels operating in southern Syria, with some moving to Turkey for rebels operating from there.
That this arms pipeline should now be in full flow comes as no surprise, with fighting intensifying daily across Syria and the rebels' need for resupply seemingly endless. The same former US official who spoke of "a cataract of weaponry," says that the quantities are huge because the rebels "burn through a million rounds of ammo in two weeks."
But as many intelligence and regional analysts are at pains to point out, the flood of weapons into Syria also comes at precisely the moment when major differences are emerging between Islamist and secular rebel forces.
It comes as one of the most combat-effective rebel groups on the ground, the powerful jihadist al-Nusra Front, last week pledged its allegiance to the leader of al-Qaeda, Ayman al-Zawahiri.
Only last month the al-Nusra Front played a pivotal role in the capture of Raqqah, Syria's first provincial capital to fall under opposition control. That victory effectively consolidated the gains of an assortment of mostly Islamist-inclined groups across three of Syria's north-eastern provinces.
In taking Raqqah the al-Nusra Front had, of course, to rout government troops loyal to Syrian president Bashar al-Assad, but in so doing it also set itself on a further collision course with other more moderately Islamist or secular rebel groups, who do not share or sometimes openly oppose the jihadist outlook of the al-Nusra front.
Among the al-Nusra Front's most dogged rivals are the Farouq Brigades, one of the largest and best- known units of the rebel umbrella organisation, the Free Syrian Army (FSA). To say that there is no love lost between these two bitter rivals would be an understatement.
In January, there was the killing of Thaer al-Waqqas, northern leader of the Farouq Brigades, amid suspicions he himself was involved in the death of a commander linked to the al-Nusra Front.
Then in March, Mohammad al-Daher, another popular Farouq leader in eastern Syria, was badly wounded in an apparent attempt to assassinate him by the jihadists.
Within hours Colonel Riad al-Assad, who established and commanded the FSA, was badly injured in a car bombing.
It was initially believed to be the work of the Syrian regime, but some now say the attack bore distinct similarities to the one on al-Daher.
All this points to a deepening rift between the al-Nusra Front and the Farouq Brigades and has profound implications not only for the CIA's clandestine arms supply programme but the future direction of Syria's civil war and its outcome.
Are we perhaps looking at a rebel war within the already ongoing one between opposition and Syrian government forces?
"A full-blown civil war among the rebels is not out of the question," was how Victor Kotsev, an experienced Middle East political analyst, summed it up in a United Press International report last week.
Blacklisted by the United States as a terrorist organisation and having confirmed its allegiance to al-Qaeda's leadership last week, the al-Nusra Front poses a major headache for the Washington administration.
On the one hand the US wants to see the toppling of President Assad, on the other, it also quickly needs to neuter the influence of the jihadist fighters – who in fact are among the most capable of taking the fight to the Syrian regime.
This takes us back to the dilemma the CIA now faces with regard to its current Syrian rebel arms supply line.
The spy agency's officers remember all too well how they supplied Afghanistan's mujahideen guerrillas with weaponry to fight the Russian Red Army in the 1980's.
Many of those same weapons later found their way into the hands of the Taliban and other jihadists.
Not surprisingly the CIA has gone to considerable lengths to prevent a rerun of this particular experience inside Syria.
This in part explains why for months after the start of the Syrian uprising, the US and others held back on arming the rebels.
Certainly there is evidence that in this initial stage of the uprising, President Barack Obama and his White House staff were more cautious, fearful that the weapons would make their way to what one US official described as the "bad guys."
The Pentagon, State Department and CIA, however, were less restrained.
Now, though, there is the growing suspicion that the decision to send increased weapons is more unanimous, and has as much to do with arming moderate or nationalist rebel groups willing to oppose the jihadists as it does with equipping those same fighters to bring down the Assad regime.
For some time the CIA's analysts at its headquarters in Langley have been concerned that the bad guys by and large have been better armed than those they see as the good guys, and the agency now seems determined to redress the balance.
But should they be hell-bent on doing so, is it not inevitable that some of their military largesse will end up among the ranks of al-Nusra and their jihadist allies?
In its detailed investigation the NYT quoted two rebel commanders, Hassan Aboud of Soquor al-Sham and Abu Ayman of Ahrar al-Sham, both "moderate" Islamist groups who claim that whoever is vetting the weapons supplies is not doing a very good job.
"There are fake Free Syrian Army brigades claiming to be revolutionaries, and when they get the weapons they sell them in trade," Aboud was quoted as saying in the NTY investigation.
Last month, the Leicester-based blogger Eliot Higgins (aka Brown Moses) blew the lid on the covert international operation to arm the Syrian opposition by discovering that a batch of Croatian weapons made their way into in the hands of Syrian rebels. He also found that Saudi-purchased weapons were turning up in the hands of jihadists all over the country.
Higgins's work on analysing Syrian weapons, which began as a hobby, is now regularly used by human rights groups and has led to questions in the UK Parliament.
Largely unpaid and working from a laptop more than 3000 miles away from Damascus, Higgins has been accused by conspiracy theorists of being in the pay of everyone from the CIA and MI6 to the Israeli intelligence service Mossad.
However, according to Peter Bouckaert, emergencies director at Human Rights Watch, who worked with Higgins to document the use of cluster bombs in Syria: "Brown Moses is among the best out there when it comes to weapons monitoring in Syria."
His work is testimony to the power of a new breed of online investigator tackling work that was once the exclusive preserve of intelligence and military specialists.
Among Higgins's revelations over arm supplies in Syria was exposing for the first time the extensive use of cluster bombs despite the Syrian government's denial that they existed inside the country. He also exposed the proliferation of shoulder-launched heat-seeking missiles known as Manpads, and their most recent use in the hands of rebels fighting around Aleppo. Perhaps most significant, however, was his discovery of a cache of weapons from Croatia in the hands of rebel groups fighting in the southern Syrian province of Deraa. Subsequent reports alleged the weapons were financed by Saudi Arabia with the knowledge of the US and CIA.
For now, many of the countries at the centre of the arms supply chain, including Croatia and Jordan, have denied any role in moving arms to the Syrian rebels, but the evidence is mounting.
As the rivalry between rebel groups intensifies in tandem with their own front-line efforts directed at ousting the Assad regime, there are growing fears that the Islamists' gains in Syria's north-eastern provinces could split the country along a north-south, Aleppo-Damascus divide – not unlike the intense rivalry in Libya between the Islamist east, centred on Benghazi, and the west, dominated by Tripoli.
On Friday the UN Security Council began informal talks on imposing sanctions on the al-Nusra Front after it pledged allegiance to al-Qaeda leader Ayman al-Zawahri.
French foreign ministry spokesman Philippe Lalliot said given Wednesday's announcement by al-Nusra chief Abu Mohammad al-Golani, it was logical to look at how to deal with the Syrian group in the framework of the "fight against terrorism".
"One option is to act at the UN Security Council ... through the al-Qaeda 1267 sanctions committee," he said.
He added: "It is one solution that we are studying and discussing informally with our UN Security Council partners and European allies." Sanctions could include assets being frozen and travel bans.
At the very least, last week's announcement by the al-Nusra Front, alongside other developments, undoubtedly confirms suspicions that the Syrian civil war is creating opportunities for international jihadists to coalesce in the region.
While the problem facing the UN will be how best to sanction these now confirmed al-Qaeda allies, the challenge facing Washington and those other sponsors of the arms supplies reaching Syrian rebels will be how best to keep such weaponry out of the jihadists' hands. Such a task seems near-impossible amidst the myriad groups that now make up the country's armed opposition.
Difficult as it is to believe, Syria's civil war looks set to get dirtier than ever.