With every day that passes, the crisis in Iraq become more intractable.

It also becomes more difficult to resolve. Each city that falls in the hands of the Sunni insurgents becomes a battleground, each person killed becomes a martyr to one side or the other, each piece of the infrastructure destroyed is another milestone in a journey that will only lead to the country's destruction.

Meanwhile, far away from the heat and dust of the Euphrates valley and the open spaces of the Kurdish north, the world's leaders wring their hands and talk about solutions. As they do so, many of them are aware that the last time they took part in a similar discourse they made the wrong decisions and created many of the problems that have led to the present impasse.

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Even those not involved in the US-led invasion of 2003 are coming under fire from those who were. On Friday, former US Vice-President Dick Cheney, deputy to George W Bush, emerged from the shadows to rail against President Barack Obama's inaction, saying: "Rarely has a US president been so wrong about so much at the expense of so many."

His attack brought an ­indifferent response from the White House, while Senate Majority Leader Harry Reid countered that "being on the wrong side of Dick Cheney is being on the right side of history."

Despite the jibes, though, there is a growing consensus around the world that the killing in Iraq cannot continue, that something has to be done not just to bring succour to the people of Iraq but to prevent the violence spiralling further out of control - not just within the Middle East, but across the wider world.

Against that background there is also a resurgence of concern that military intervention is not always the best solution. Since coming to power in 2009, President Barack Obama has announced the withdrawal of the bulk of US troops from Afghanistan by the end of this year and managed to keep the country out of possible interventions in Libya and Syria. From being the flavour of the month in 2003, interventionism is now deeply out of fashion.

With that in mind, perhaps the most interesting observation last week came from Condoleezza Rice, formerly Bush's national security adviser but now a professor at Stanford University. "Let me just assure you that today's headlines and history's judgment are rarely the same," she said while visiting the State Department in Washington to unveil her official portrait.

Option 1: US Intervention

Beyond the rhetoric, the US remains the only global power that has the reach and the weapons to intervene in Iraq. Nothing will happen until Secretary of State John Kerry arrives in Baghdad later in the month with a team of security advisers to assess the situation, but that does not mean that nothing is already taking place.

From the outset of the crisis, US drones have been busy flying over Iraq collecting intelligence and monitoring the action on the ground. It has also become clear that special forces teams are already in the country. Add the collection of signals intercepts, satellite surveillance and the collation of human intelligence and it is clear that US forces are probably well placed to move quickly and efficiently into Iraqi territory. It would be a surprise if they were not.

The water was muddied last Thursday when Obama seemed to suggest US support would be conditional on the government of President Nouri al Maliki taking steps to become more inclusive, a call that was echoed by Grand Ayatollah Ali al Sistani, Iraq's senior Shia cleric, who claimed his country needed a new government that avoided "past mistakes".

However, by the end of the week the White House was distancing itself from that absolutist stance as it became known that Obama had sanctioned the employment of 300 special advisors to give back-up to the beleaguered Iraq army.

Innocuous in itself - US advisors operate in trouble-spots all over the world - the decision does carry the risk of mission creep. It also brings with it the threat of US involvement in operations to counter the steady advance of the fighters of the Islamic State of Iraq and the Levant (Isis) who are engaged in fierce battles for the strategically important Baiji oil refinery and the Tal Afar airport in northern Iraq.

As Iraqi government forces ­struggle to counter them, it is always possible the fighting will degenerate into the kind of heavy-handed operation that disfigured the civil war in neighbouring Syria as soldiers, insurgents and civilians became indistinguishable on the front line. All it would take would be evidence of a US missile strike or the presence of US special forces to give Isis an unmistakable propaganda victory.

Option 2: Help from the neighbours

On the face of it, the country with most to lose in the current crisis is Iraq's powerful neighbour Iran. Not only is it a regional power in its own right, with ambitions to become a nuclear state, but its Shia majority government has both a religious and political incentive to support Maliki's government. It is no secret that Iranian military advisors from the elite Republic Guards have already been operating inside Iraq.

That fact, together with a softening of Iran's recent hard-line stance, has led to rumours there could be an unholy alliance between Iran and the US, the country apostrophised as the "Great Satan". After years of confrontation between the US and Iran, such a rapprochement has a comforting ring. It might also help find a solution to the vexed question of Iran's nuclear status, which is due to be settled on July 20, but a formal declaration of friendship or even unofficial military co-operation on the ground seem unlikely.

While the old diplomatic dictum remains true that "my enemy's enemy is my friend", Iran has too many differing goals in the region to jump into bed with Washington. For a start, it is suspicious of US motives, especially after Obama called for the reform of Maliki's government. Whatever else the Iranians might feel about the current position, the Iraqi leader is not only a fellow Shia but he has allowed his country to be a conduit for Iranian arms to flow into Syria to support the regime of President Bashar al Assad. If that were to be discontinued, the long-running civil war inside Syria could become ever worse as Isis fighters flood into the country to fill the vacuum.

Then there is the whole weight of history. Iran and the US have been at loggerheads for over 30 years and the mutual suspicion and hostility will not disappear overnight. It is not so long ago that a US president called Iran part of the "axis of evil" (the other two parts being North Korea and Iraq). Then there is the ambivalent position of Saudi Arabia. It is a key US ally in the Middle East and an important power-broker, but King Abdulla of Saudi Arabia will not co-operate in any way with Iran, which is regarded as too powerful a supporter of Maliki to be trusted.