Washington wants to refine its military partnership with Seoul

Mr Rumsfeld told a Pentagon meeting that some of the 37,000 troops could be moved further south, sent to neighbouring countries, or even sent home.

A spokesman for the US Forces Korea command centre in Seoul said that Washington was considering the shake-up as part of an attempt to modernise the US-South Korean military alliance.

The US troops are "all in the same place that they were when the (Korean) war ended 50 years ago", Lieutenant-Colonel Mike Caldwell told BBC News Online.

Of the total US force, 28,000 are army troops, many of them stationed near the Demilitarised Zone [DMZ] which separates the two Koreas. Of this total, 15,000 are deployed north of Seoul.

Main US bases in South Korea

The possible redeployment would be in accordance with a Land Partnership Plan ratified in South Korea in October 2002.

The agreement entails the reduction of the US' military bases from 41 to 23 over an 11-year period, although not necessarily a reduction in the number of personnel.

Such a plan, Lieutenant Caldwell said, would free up more money to improve the military infrastructure, and enable Washington to hand land back to South Korea.

US-South Korean relations have been strained in recent months by a number of high-profile incidents involving US troops, including the acquittal by a US military court last year of two US soldiers who ran over two South Korean schoolgirls.

While the plan to modernise the US operation in South Korea was drawn up before the incident, Washington's plans may help to mollify anti-US protesters in the country.

Professor Chung Min Lee, a specialist in security issues with the Department of International Relations at Yonsei University in Seoul, told the BBC that "rising anti-Americanism was a key factor" in the review of the US forces' role.

But Mr Rumsfeld's comments also come at a time of high tension on the Korean peninsula concerning North Korea's nuclear activity.

South Korean Prime Minister Goh Kun urged the US on Thursday to delay talks on refiguring its military presence.

At a meeting with US Ambassador Thomas Hubbard, Mr Goh said it would be "inappropriate to talk about redeploying US troops at this time, given the tension surrounding the nuclear issue".

"The role of the US troops as a trip wire must be maintained," he added.

However, Mr Lee said that there was disagreement about exactly how robust a US force needed to be maintained.

He pointed out to the World Today programme that South Korean President Roh Moo-hyun said this week that the recent North Korean tailing of US fighter jets appeared to be a reaction to an increase in American surveillance.