Approximately 20 people are being questioned by US forces in Iraq on suspicion of having links to al-Qaeda.
Lieutenant General Ricardo Sanchez, the Commander of US forces, did not say where the men were detained. He added no proof has yet been found.
The move comes as Iraq's US governor, Mr Paul Bremer, left the country at short notice this afternoon - cancelling a meeting today with visiting Polish Prime Minister Leszek Miller, the Polish delegation said. There was no immediate explanation for the move.
The United States has been pushing for other countries to send troops to help secure Iraq and is also trying to give more responsibility for security to Iraqi police and troops.
Defense Secretary Donald Rumsfeld said last nightWashington was not looking for an exit strategy and that his top commanders had assured him the insurgency was under control.
The Pentagon last week announced a plan to reduce US forces in Iraq to 105,000 by next May and has said the number of Iraqis serving in security forces will soon exceed the American troop presence in the country.
"The goal is not to reduce the number of US forces in Iraq," Mr Rumsfeld said. "It's not to develop an exit strategy. Our exit strategy in Iraq is success. It's that simple."
Mr Rumsfeld and President George W. Bush are coming under political pressure due to the mounting US death toll in Iraq and the failure to find any weapons of mass destruction.
A group of more than two dozen House of Representatives Democrats said today they had introduced a resolution urging Mr Bush to fire Mr Rumsfeld.