The Bush administration has accused the EU of "actively undermining" American efforts to protect its peacekeepers from prosecution by the international criminal court, which was set up to try cases of genocide, war crimes and systematic human rights abuses.
A note written by a US official says Europe's objections "will undercut all our efforts to repair and rebuild the transatlantic relationship just as we are taking a turn for the better after a number of difficult months", according to the Washington Post. "We are dismayed that the European Union would actively seek to undermine US efforts."
The row began in April when the EU issued a letter to prospective members urging them not to sign up to bilateral agreements with other countries granting them broad immunity from prosecution.
The US, which was seeking such agreements with many eastern European countries, regarded the letter as hostile.
EU officials insisted that they had a right to enforce union policy with candidate countries and denied any hostility towards the US. "The Americans see this as a campaign against them, but it's just a question of how we see things," said one.
Under an agreement reached last year, American peacekeepers are exempt from trial or arrest by the ICC because Washington fears the court could be used for frivolous or politically motivated prosecutions of its troops.
The agreement, which is backed by the EU, is up for renewal tomorrow at the security council. Despite opposition from Germany and France, the resolution extending the exemption will be adopted, as there is little stomach for another bruising row with the Bush administration, although it is not clear whether some countries will use their veto.
Last year's vote was 15-0 after the US threatened to veto UN peacekeeping missions, one by one.
America is said to have been threatening some Balkan countries with a withdrawal of aid if they do not sign bilateral deals. Last month Albania became the third European country, after Romania and Georgia, to sign a deal.
Now Macedonia, Bosnia, Croatia and Serbia and Montenegro have been told to follow suit or lose US aid and support.
The US has so far signed agreements with 37 countries worldwide.
Defending the union's appeal to eastern Europeans, an EU diplomat said: "You can hardly describe this as heavy-handed pressure. Unlike the Americans, we have not threatened to disrupt funding."
In response to pressure from Washington, Spain was seeking last night to persuade fellow EU members to tone down attempts to prevent bilateral agreements being signed.
"The European Union is asserting the principles they have adopted and urging those states that want to join the EU to keep those principles in mind," Richard Dicker of the New-York-based advocacy group Human Rights Watch told the Washington Post.
"It's the US putting those governments that have ratified the treaty between a rock and a hard place."
Jose Maria Aznar, the Spanish prime minister, was one of President Bush's strongest supporters during the Iraq war. Britain and Italy have also been seeking to avoid a new row before the EU-US summit this month.
"There are a number of member states who are very keen not to antagonise the US on this issue and want a softer line," an EU official said.
