Rumsfeld is not known for mincing his words
The United States has renewed controversy within Nato over Belgian legislation which makes foreigners vulnerable to prosecution for alleged war crimes.
American Defence Secretary Donald Rumsfeld warned that Washington would block further funding for Nato's new headquarters in Belgium until the legal threat was withdrawn.
US authorities have been outraged by complaints brought against General Tommy Franks - who commanded US forces in the Iraq war - and other officials under laws that allow Belgian courts to try war crimes wherever they are committed around the world.
In another development on Thursday, the United Nations Security Council granted US peacekeepers another year of immunity from prosecution by the International Criminal Court (ICC) by 12 votes to none.
Speaking after a meeting of Nato defence ministers in Brussels, Mr Rumsfeld said it did not "make much sense to make a new headquarters if you can't come here for meetings".
According to the BBC's Jonathan Marcus in Brussels, it was an unusual and blistering attack upon one of America's Nato allies - a sign that there are still some serious tensions that from time to time break through to the surface.
The case against General Franks was filed by a left-wing lawyer on behalf of a group of Iraqis injured or bereaved in the war.
It followed similar complaints brought against former President George Bush, Vice President Dick Cheney and
Secretary of State Colin Powell for their role in the first Gulf War.
Reacting to the US outcry, the Belgian Government rushed changes to the laws through parliament which mean
any such complaints can be transferred to the country of
the accused if that nation has a fair and democratic legal system.
The war in Iraq has heightened the Pentagon's sensitivity
Prime Minister Guy Verhofstadt referred the General Franks case
back to the US last month, although the attorney Jan Fermon is appealing on behalf of the 19 Iraqis bringing the case.
Belgian Defence Minister Andre Flahaut said he was
surprised by Mr Rumsfeld's warning, insisting the General Franks case
had been rejected by his country.
Mr Rumsfeld has said American military and civilian officials
need assurances they could come to Brussels without facing
"harassment" from the Belgian courts.
The US itself put forward the UN Security Council resolution which extends the immunity of states which have not ratified the ICC's founding statute from its jurisdiction for a second year from 1 July.
Reach of ICC
90 countries have ratified the Rome treaty that established the court
139 countries are signatories to the treaty
The extension was approved grudgingly as almost every speaker in the debate highlighted the unlikelihood of US peacekeepers ever being in a position where they were prosecuted by the court.
Three of the 15 Security Council members - France, Germany and Syria - demonstrated their disapproval by abstaining.
Earlier, UN Secretary General Kofi Annan warned that the legitimacy of peacekeepers would be undermined by recurrent extensions to their immunity from the jurisdiction of the ICC - the world's first war crimes court.
America is also currently drawing up agreements with individual governments which bar them from surrendering US nationals to the court and has signed nearly 40 such agreements to date.
The deputy US Ambassador to the UN, James Cunningham, welcomed the approval of his resolution but added that, "like any compromise, [it] does not address all our concerns".
Germany, a principal proponent of the court, said its abstention was "a matter of principle".
Even the UK indicated it had differences with one of its closest allies over the issue.
"Whilst we understand US concerns about the International Criminal Court, we do not share them," said its Ambassador, Sir Jeremy Greenstock.