Washington ? The number of prisoner deaths in Iraq and Afghanistan known to be under U.S. criminal investigation or already blamed on Americans rose to as many as 14 on Wednesday. Defense Secretary Donald H. Rumsfeld was called to testify before Congress Friday on the prisoner abuse and its ramifications.

And new focus was put on the question of possible deeper problems within the military police unit running the Abu Ghraib prison in Iraq.

Rumsfeld will testify to the Senate Armed Services Committee, whose chairman, John Warner, R-Va., said he had confidence in the secretary. But some Democrats seemed less sure.

Sen. Joseph Biden, D-Del., said that if adequate answers to questions about the abuse of prisoners were not forthcoming, then top officials, including Rumsfeld, should step down.

“If it goes all the way to Rumsfeld, then he should resign,” Biden told the “Today” program on NBC. “Who is in charge?”

Coupled with the Iraq war’s mounting death toll — it rose to 758 U.S. troops on Wednesday, according to the Pentagon’s count — and rising financial costs of the war, the prisoner abuse story has become a major political burden for the White House during an election year.

The Army had disclosed on Tuesday that its Criminal Investigation Division was probing 10 prisoner deaths and that two other deaths already had been ruled homicides. On Wednesday, an intelligence official said the CIA inspector general was examining two additional deaths involving agency interrogators.

It was not clear if there was overlap between what the CIA and Army announced, and officials said they could not clarify the numbers.

It also was not clear Wednesday whether the June 6 death of an Iraqi prisoner at a U.S. military detention facility near the city of Nasiriyah, for which two Marines face a court-martial, is among the cases cited.

There was considerable evidence that the abuse incidents were not isolated occurrences.

When Lt. Gen. Ricardo Sanchez, the senior American commander in Iraq, ordered an investigation in January into reports of prisoner abuse and other issues at Abu Ghraib prison, he said there appeared to be systemic problems within the military police unit running the prison.