Prime Minister Tony Blair's eldest son Euan will work as an intern with Republican staff in the U.S. House of Representatives, the prime minister's office said on Sunday.

Euan, 21, will spend three months working with a committee which determines how U.S. legislation is considered in the lower chamber of Congress.

"Euan Blair has been given the opportunity to take up a short, unpaid internship with the Rules Committee of the House of Representatives," said a spokesman at the prime minister's Downing Street office.

Despite Blair's close relationship with U.S. President George W. Bush, the news raised eyebrows among some Democrats who see Blair's Labour party as natural allies, reported the Sunday Telegraph newspaper.

"It is extremely surprising that the son of a Labour prime minister would intern with the Republican majority staff on the committee," the paper quoted Eric Burns, communications director for Congresswoman Louise Slaughter, the committee's leading Democrat, as saying.

The newspaper said Euan would be mentored by David Dreier, a Californian representative to the Republican leadership in the House, during his internship.

The Downing Street spokesman said Euan was also hoping for an internship with the Democrats.

The news comes a few weeks after Blair's wife Cherie came under fire for giving a well-paid speech in Washington at the same time as the Prime Minister visited the White House.