The US fears its soldiers could be vulnerable to malicious prosecution
The United States has suspended over $47m in military aid to 35 countries that have not signed deals to grant American soldiers immunity from prosecution for war crimes.
State Department spokesman Richard Boucher said the protection of US citizens from the threat of being hauled before the new International Criminal Court (ICC) was a significant matter in relations with other countries.
The US does not recognise the ICC, saying its forces could be subjected to politically-motivated prosecution.
One country which is particularly affected in Colombia, which receives over $500m a year in US military assistance.
The new court, based in The Hague in the Netherlands, can try individuals for war crimes committed after 1 July anywhere in the world.
Washington has concluded bilateral agreements with more than 50 nations to secure exemption for US troops.
Human Rights Watch has accused the US of bullying tactics in its efforts to conclude exemption deals.
"US officials are engaged in a worldwide campaign pressing
small, vulnerable and often fragile democratic governments," it said in a letter to US Secretary of State Colin Powell.
Nato members and other key allies - such as Israel, Japan, South Korea, Australia and New Zealand - are exempt from any penalty if they
In implementing the act, we'll need to balance our broader bilateral interests with substantial consideration to the risk posed to US citizens
State Department spokesman
Others face cuts in military aid, under the American Service members Protection Act approved last year by the US Congress.
However Mr Boucher said the US administration might waive the aid suspension for countries regarded as crucial to Washington's strategic interests.
"In implementing the act, we'll need to balance our broader bilateral interests with substantial consideration to the risk posed to US citizens... by the potential for politically motivated charges," he said.
Colombia could be a case in point, since US support in the fight against the cocaine trade means it receives more funding than any other Latin American country.
It has received almost all the aid allocated for 2003, but a halt to 2004 military funding would be crippling.
State Department figures suggest that of the $575m requested by the Bush administration for next year, about $112m would be blocked.
"You can bet that all these problems are going to be cleared up," said Defence Minister Marta Lucia Ramirez.
Colombia says that a 1962 agreement already provides immunity for the hundreds of US personnel training anti-narcotics squads in the country.
But Mr Boucher said that treaty did not provide the exemption required by law.
The BBC's Gabriel Partos says that the American demand for immunity from war-crimes prosecution has created a particular dilemma in the Balkans.
South-east European countries welcome Washington's military aid, but are also under pressure from the EU - a strong backer of the ICC - not to conclude immunity deals.
Bulgaria, which has not signed a deal, was told on Tuesday that half of its promised $20m in aid would be suspended.
Bulgarian officials said that discussions on the issue were continuing, and did not rule out the eventual signing of a bilateral agreement.
Croatia, another EU candidate state, has refused to sign such an agreement for the time being.
Others, including Romania, Albania, and Bosnia-Hercegovina, have granted immunity to US forces.