By Paul Reynolds
World Affairs Correspondent, BBC News website
How long will coalition troops remain in Iraq?
The chaos that has overtaken Iraq is now threatening hopes among the US and its allies that they might be able to start significant troop withdrawals in the coming months.
Such withdrawals have always been conditional on the security situation and that situation is, to say the least, on a knife-edge following the bombing of the Shia al-Askari shrine in Samarra and the subsequent retaliations.
Australian Prime Minister John Howard has already publicly expressed his concern over the effect of increased sectarian tensions on embryonic troop withdrawal plans.
"There's no early prospect of all coalition forces being withdrawn, although until this latest event the signs were looking good," he told Australian radio.
The foreign forces are now in a predicament - their presence adds to the violence yet they are not withdrawn for fear that the violence might get worse. They are part of the problem and not enough of the answer.
I say "part of the problem" because the attack on the shrine indicates that something else is going on in Iraq beyond getting the troops out.
The Sunni-led insurgents, or at least the powerful Islamist elements among them, want to turn on the Shias, their religious rivals. The departure of US troops would, of course, make this much easier.
This is no great surprise. The insurgents have bombed Shia gatherings before, though this bombing is a step up because it symbolically attacks a whole branch of Islam.
Remember what the al-Qaeda leader in Iraq, Abu Musab al-Zarqawi, wrote in an intercepted letter two years ago.
According to the text released by the US State Department, he had this to say about the Shias: "[They are] the insurmountable obstacle, the lurking snake, the crafty and malicious scorpion, the spying enemy and the penetrating venom.
"We here are entering a battle on two levels. One, evident and open, is with an attacking enemy and patent infidelity. [Another is] a difficult, fierce battle with a crafty enemy who wears the garb of a friend, manifests agreements and calls for comradeship, but harbours ill will and twists up peaks and crests."
Zarqawi's first enemy is the "evident and open" foreign invader, the second is the "crafty" one - that means the Shias.
The issue now is whether Iraq will plunge into outright civil war, whether it will pull back from the brink and find some political modus vivendi, or whether this kind of low- to middle-intensity civil conflict will continue for the foreseeable future.
In any event, at the moment, neither of the two elements needed before a foreign withdrawal can happen are in place.
The issue now is whether Iraq will plunge into civil war
There is neither a functioning government nor security.
The bombing could either make forming that government even more difficult or help forge compromises.
The interventionist US ambassador in Iraq, Zalmay Khalilzad, had already warned the majority Shia political leaders not to squeeze out the minority Sunnis and not to run their security agencies along sectarian lines, otherwise US funds would dry up.
It remains to be seen therefore if and when an effective government can be formed.
'On the edge'
On the security front, the figures do not point towards much progress.
The Iraq Index of the Brookings Institution in Washington estimates that the number of Iraqi civilian deaths varied between roughly 600 and 1,000 over the past couple of months - about the same level as this time last year.
Iraqi troops still need the support of coalition forces: Jeremy Greenstock
Iraqi security force deaths were 104 last month, much as a year ago, though lower than in the summer.
US troop fatalities from hostile incidents were 84 over the past two months, slightly higher than this time last year but again lower than a few months ago.
This has an impact on the prospects for foreign troop withdrawals.
"If they left, in the short term there would be an increase in violence," said Sir Jeremy Greenstock, who was British representative on the Coalition Provisional Authority (CPA), which ran Iraq under occupation after the 2003 invasion.
"I think they are necessary for the Iraqi security forces. The army is not yet fully formed and the police are not effective at the moment," he told the BBC.
I remember Sir Jeremy being quite optimistic when he was on the CPA. He used to talk about Iraq being "do-able". Now he is much more pessimistic.
"Without foreign help, Iraq would fall apart much more quickly," he said. "It is on the edge and we do not know if it is going to succeed."