But while maintaining pressure over the EU drive to lift its 15-year-old embargo, Washington conceded it was unclear what measures Washington would take if, as expected, the ban were lifted in the next few months.

"We're quite united, the (US) administration as well as the Congress in the fact that we don't like the fact of the lifting of the arms embargo," said the official.

"But as far as specific measures (which could be taken by Washington if the EU lifts its ban) that is certainly not clear at this stage," he added.

The EU ban was slapped on Beijing after the 1989 Tiananmen Square massacre. The EU move to lift it has been led by France, which argues it is outdated given the political changes in Beijing over the last decade and a half.

The United States is worried that lifting it could help China build up its military, in particular threatening the military balance between China and Taiwan.

Last week US lawmakers, after being briefed by US President George W. Bush following his trip to Brussels last month, warned about "potential repercussions for trade" if the arms embargo is lifted.

Richard Lugar, chairman of the US Senate Committee on Foreign Relations, made it clear that trade restrictions were an option.

"I suspect there would be prohibition on a great number of technical skills and materials or products available to Europeans. It could change very much some multinational business plans," he said.

The EU is justifying its planned end to the embargo by proposing a self-imposed code of conduct on arms sales, and is trying to convince the US that this will be effective.

"The burden is on the EU side to make that case," said the US official in Brussels.