U.S. lawmakers are demanding an explanation from the Bush administration about allegations that U.S. military police abused Iraqi prisoners.

The Republican-led Senate and House Armed Services Committees held closed-door briefings with Army officials to discuss the alleged abuse of Iraqi prisoners. The top Democrat in the Senate, Senator Tom Daschle of South Dakota, called on Defense Secretary Donald Rumsfeld to brief lawmakers on the matter.

He spoke on the Senate floor. "I come to the floor with grave concern about the news, about the events, about the message it sends, about the extraordinary impact it has had on our efforts to succeed in that country, about the violation of human rights, [and] about our appalling inability to explain how this happened," he said.

Photographs televised around the world showing Iraqi detainees apparently being sexually humiliated and physically abused have prompted outrage in the Muslim and Arab world.

Republican Senator Susan Collins of Maine said that she is concerned the images could incite more violence against U.S. troops in Iraq.

At the White House, spokesman Scott McClellan said that President Bush has discussed the matter with Mr. Rumsfeld and ordered an investigation.