A war with Iraq would cost the US and its allies considerably less than the 1991 Gulf War, a leading international think tank has said.

The International Institute for Strategic Studies put the cost of a war with Iraq for the US at roughly half the cost of Operation Desert Storm in 1991.

Cost of war

1991 Gulf War: US: $61bn UK: $4.1bn 2003 conflict: US: $33bn UK: $5.5bn

The think tank also looked at the cost of a possible reconstruction of post-war Iraq, an element that has received little attention so far.

An ambitious 'Marshall Plan' for the build-up of post-war Iraq could cost the US and its allies up to $75bn (�45.8bn) for a six-year period, the Institute said.

A peacekeeping force ranging from 50,000 to 200,000 in Iraq could cost between $12bn and $50bn a year alone.

The think tank based these numbers on the costs of a peacekeeper in Bosnia, which amounts to $250,000 a year.

A five-year presence by 100,000 troops in Iraq could add $125bn to the bill.

The Institute said it was difficult to forecast the precise cost of a military conflict, because much of the total costs depend on the length of the conflict and the scale of the Iraqi resistance.

British burden

For the UK, America's strongest ally in the ongoing stand-off with Iraq, the costs of a new conflict would be roughly equivalent to those made in 1991, when adjusted for inflation.

The $5.5bn figure would be in addition to the $39.7bn annual British defence budget.

Peacekeeping could cost up to $50bn

The UK has said it is sending some 43,000 troops to the Gulf.

Last week, American president George W. Bush proposed a $380bn defence budget.

This figure did not include a provision for a possible conflict with Iraq.

Heavy ground option

In 1991, the US was reimbursed for about 90% of its costs by its allies, including Saudi Arabia, Kuwait, Japan, Germany and South Korea.

During the first Gulf War, some 500,000 US troops were deployed in the Gulf Region.

The Institute said that the costs of a new conflict would be much lower because fewer troops will be sent.

A smaller force, known as the 'Heavy Ground Option' would consist of five army divisions, instead of eight during Desert Storm.

Thus, transport costs will be significantly lower.

Further, costs would be lessened because of the ongoing policing of the no-fly zones in the north and south of Iraq.

This has led to fewer targets than in 1991, reducing the number of munitions required.

Finally, most personnel and equipment used during Desert Storm had to deployed from a 'standing start', whereas in 2003 the US already has a substantial military presence in the Gulf Region.