And so it escalates.
Where it is ultimately heading, of course, is anybody's guess, but the signs of all-out war in eastern Ukraine have been there for some time.
Russia's denials of direct military involvement on Ukrainian soil have long since worn thin. Nato's continued use of the word "incursion" to explain away that same Russian involvement now also has an empty ring to it.
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That much was clear on Friday when Nato Secretary General Anders Fogh Rasmussen finally bit the bullet and called the situation as he saw it.
"Despite Moscow's hollow denials, it is now clear that Russian troops and equipment have illegally crossed the border into eastern and southeastern Ukraine," Rasmussen said. "This is not an isolated action, but part of a dangerous pattern over many months to destabilise Ukraine as a sovereign nation."
Samantha Power, the US ambassador to the United Nations was even more pointed in her assessment.
"The mask is coming off," she insisted.
"In these acts we see Russia's actions for what they are: a deliberate effort to support, and now fight alongside, illegal separatists in another sovereign country."
Lithuanian president Dalia Grybauskaite added that Russia is now effectively at war with Europe. "Russia is in a war state against Ukraine," she said. "That means it is in a state of war against a country which would like to be closely integrated with the EU. Practically Russia is in a state of war against Europe."
For its part, Ukraine's government, perhaps sensing a substantial diplomatic shift among Western powers and one too on the battlefield, says it is now abandoning Ukraine's non-aligned status and is setting the country on a course to become a member of Nato.
President Petro Poroshenko said Ukraine was a victim of "military aggression and terror", adding: "I think that we are very close to the point of no return. Point of no return is full-scale war. Any offensive action which would be undertaken [by Russia] ... would be a point of no return. And that's why we undertake enormous efforts to stop that."
So, the regional and international battle lines are being drawn up, but just what, exactly, has been happening on the ground in eastern Ukraine of late? What too can we make of the Kremlin's latest moves and what it tells us about the long-term aims of Russian president Vladimir Putin? As the fighting in eastern Ukraine has intensified, forces loyal to Kiev have faced relentless opposition from pro-Russian separatist groups heavily supported and reinforced by Moscow. Access to supplies has been one of the major factors in these ongoing battles, and both sides have fought hard to keep the logistic routes open and functional.
In some instances cracks in Ukrainian military performance and battlefield capabilities are beginning to show, placing significant pressure on Poroshenko and his government.
In the past week, Russian troops have attempted to relieve pressure on their separatist allies in Donetsk and Luhansk by opening what amounts to a third front south of the two breakaway cities.
Meanwhile, Ukrainian troops, who had been steadily advancing on separatist forces in the east, were forced to make a rapid retreat from Novoazovsk, where they were routed by troops and armour streaming across the Russian border.
On Friday alone, 10 Ukrainian soldiers were killed and 30 wounded in fighting. According to a senior United Nations human rights official, a total of 2593 people have now died in fighting in eastern Ukraine since mid-April.
Novoazovsk itself lies barely 20 miles from the southeastern port city of Mariupol, a city with nearly 500,000 inhabitants.
These latest advances, have left some Western officials fearing that Moscow is trying to carve out a land bridge to the Crimean peninsula, which it annexed earlier this year.
The key question in turn, say some analysts, is whether president Putin aims to go even further, potentially all the way to the breakaway region of Transnistria in Moldova, or is this simply a tactical move to ensure the survival of Putin's proxies in the key eastern Ukrainian cities of Donetsk and Luhansk?
According to analysts at the US-based independent intelligence monitoring group Stratfor, Ukraine's military reserves will be critical in containing any further separatist advance as well as maintaining the effectiveness of any offensive.
Increasingly the Kiev government has become reliant on the capabilities of volunteer forces and National Guard units, even if these are simply comprised of armed civilians who receive minimal training before being pushed into the frontlines.
By contrast, the separatists are backed by the Russian military, which has deep layers of trained reserves stationed in Russia, allowing for the rotation of fighters inside defended areas in eastern Ukraine.
The scale and sophistication of Russian military support has been highlighted by Joseph Dempsey, a military analyst at London's renowned International Institute for Strategic Studies (IISS).
From video footage taken last week in Sverdlovsk, Luhansk, in eastern Ukraine, Dempsey identified a Russian tank in a separatist column he said could only have come from across the border in Russia.
The footage shows a mixed convoy of tanks and other vehicles, but it is the surprising appearance of a lone, more modern tank, a variant of the T-72, that caught the attention of the IISS analyst.
Distinctive by the arrangement of Kontakt-5 Explosive Reactive Armour (ERA) plates on the turret front, the tank is commonly referred to as the T-72BM.
"The Soviet-era tanks operated by the separatists have until now represented those that could have been potentially acquired internally within Ukraine, providing a degree of plausible deniability to any suspected third-party supplier," says Dempsey. "The most recent separatist variant however, is assessed to have been operated only by the Russian Army."
Important as Dempsey's observations are, Nato Secretary General Rasmussen's unequivocal remarks on Friday detailing direct Russian involvement, has effectively eradicated any doubts about Moscow's role.
Not that Putin seems much bothered. For some, the Ukraine conflict has evoked many memories of the Cold War, including a footloose attitude to the truth. Russian involvement remains a fiction, according to the Kremlin. For Putin denying a Russian role helps keep his domestic audience in ignorance of a war they don't want, something especially useful if things begin to go wrong on the frontline.
Some European powers too have been reluctant to paint what is happing in the region as an out-and-out war between Russia and Ukraine. For them, stating that Russia has attacked Ukraine would force them to impose more costly sanctions, and could block the path to a truce with Russia they hope will resolve the crisis.
According to many world watchers, the crisis in Ukraine has been a colossal failure of analysis and of diplomacy, with plenty of blame to share on all sides.
"I think the United States and the West played a key role in causing the crisis, mostly by failing to anticipate that Russia was going to respond forcefully to what it regarded as a gradual attempt to incorporate Ukraine into the West," says Stephen M Walt, professor of international relations at Harvard University. Writing in the prestigious Foreign Policy magazine, Walt pointed out that the United States and its allies have followed a familiar pattern, ramping up sanctions and waiting for Moscow to cave and give them everything they want.
Unfortunately, insists Walt, this failed to recognise that Russia does have valid reasons to care about its border and still has cards to play. His views are endorsed by Jonathan Eyal, international director at the British think tank, Royal United Services Institute. "Putin has been, throughout this crisis, a bit of a gambler. We underestimate the element of improvisation within the Russian decision-making," says Eyal.
In the short term at least, it appears that Putin is simply aiming to prop up the separatists he backs. In the longer play, Putin clearly remains determined "to prevent Ukraine from falling into the Western sphere of influence", Eyal concludes.
In order to achieve this, Putin, despite the damning evidence to the contrary, will continue to deny that Russian troops or military equipment have attacked Ukraine.
The Kremlin knows that an all-out war would threaten Putin's popularity after an August 26 opinion poll by Russia's Public Opinion Foundation showed only 5% of respondents favoured sending Russian troops to Ukraine. If the Kremlin were to let the broader Russian public know its soldiers were fighting there, it could unearth traumatic recollections of past conflicts.
Memories are still raw of the long, drawn-out fight against separatists in the Russian region of Chechnya, and before that the Soviet invasion of Afghanistan, and the telegrams telling families that their sons had died in those campaigns.
It is interesting too that the same poll revealed that the majority of Russians receive their information on the conflict from television. This is almost entirely state-controlled and makes no mention of Russian troops fighting in Ukraine, yet 73% of respondents believed the information they get from the media is reliable.
In weighing this up, it is worth remembering that Putin only acknowledged that Russian troops had occupied Ukraine's Crimea Peninsula earlier this year after it became clear Kiev would not fight back against Moscow's annexation.
"Nobody judges the winners," said Dmitry Oreshkin, a political analyst who is often critical of Putin.
"If it's an all-out war against Ukraine, people's minds would turn around much more quickly," observes Oreshkin. "That would be dangerous for Putin."
For now the fighting continues, Putin maintains deniability and all the while Nato and the EU are looking for ways to ratchet up the pressure on Russia.
On Friday, Dutch prime minister Mark Rutte made it clear that the sanctions "have not worked" in changing Moscow's behaviour in eastern Ukraine and that additional measures must be considered by the EU. How quickly its seems that the shooting down of Malaysia Airlines flight MH17 by groundfire from separatist-held territory in eastern Ukraine has dropped off the political radar.
A total of 196 Dutch nationals were among the 298 passengers and crew on board. In light of this, Dutch insistence on calling for stronger measures against Moscow is understandable. It will be interesting indeed in the coming weeks to see just what form these measures take and what Putin's response will be to them.