At a signing ceremony in Massachusetts, Mr Delahunt - a Democrat who helped broker the deal - rejected suggestions that it was politically motivated.

"This is a gesture about people," the Associated Press news agency quotes him as saying.

"It has nothing to do, as far as I'm concerned, with anything between the Bush administration and the Chavez administration."

A moment later, Mr Delahunt covered his mouth with one hand while holding the other in front of his face. He then turned from the crowd and appeared to be shaking with what most observers described as profound emotion. With a deep sigh he returned to face his audience and, flushed, begged pardon for the interruption.