Pentagon figures indicate the number of U.S. troops wounded also dropped, USA Today reported Friday. Officials attribute the relative calm to a cease-fire agreement between Shiite rebel cleric Moqtada Sadr and his militia, which faced steady military pressure from U.S. and Iraqi troops.
So far, the least deadly month of the five-year war was February 2004, when 21 U.S. military personnel were killed in a 29-day period, the Pentagon said.
"We're seeing progress because we're getting more capability out of the Iraqi security forces," said Lt. Gen. Lloyd Austin III.
The U.S. death toll in May 2007 was 126.
Injuries among U.S. troops also were lower with 31 solders hurt in combat last week, the Pentagon said, down from a recent high of 130 in one week in March.
The number of Iraqi security personnel and civilian casualties also fell, USA Today reported. Seventy-eight people died in bombings throughout Iraq in April, the lowest number since November 2004, when 75 died, said the Brookings Institution, a Washington think-tank tracking the data.