$20bn for war and now a $2bn monthly bill

The war in Iraq has already cost the United States around $20bn (£12.7bn) – $3bn of that in munitions – and the cost of keeping troops in the country will run at $2bn a month, the Pentagon says.

These figures appear to be within expectations implicit in the $75bn requested by the White House in March for the next six months, and approved, with some extraneous additions, by Congress before its Easter recess.

But the ultimate financial burden for Washington is unknowable, and will depend on how conditions develop inside Iraq, and the degree to which US allies, many of them opposed to the war, are prepared to help in the aftermath.

The biggest uncertainty is the size of the peacekeeping force needed as post-Saddam Iraq moves towards what the Bush administration hopes will be a stable and democratic state.

General John Shinseki, the US Army Chief of Staff, astonished Congress and enraged his civilian superiors by telling a Senate committee that up to "several hundred thousand" men might be needed. Within hours, the Deputy Secretary of Defence, Paul Wolfowitz, described that estimate as "way off the mark". Even so, Pentagon planners acknowledge that the US military is already preparing the groundwork for an extended stay, either alone or accompanied by forces from Nato. Nor have US forces even moved into all parts of Iraq.

"I wish I could say this was winding down, but I can't. A lot more work remains to be done," General Richard Myers, chairman of the US Joint Chiefs of Staff , said yesterday.

The US is expected to set up some form of military headquarters in Iraq and the military commander, General Tommy Franks, will probably divide the country into separate sectors looked after by the US Army, Marines and other Allied forces.