Baghdad --

Under increased pressure from the United States, an Iraqi crackdown on Iranian-backed Shiite militias has helped produce a previously elusive goal: For the first time since the U.S. invasion of Iraq, an entire month has passed without a single U.S. service member dying.

The milestone is particularly remarkable because it comes after 14 troops were killed in July, making it the deadliest month for the Americans in three years. And it has occurred amid a frightening campaign of suicide bombings and assassinations from Sunni insurgents that killed hundreds of Iraqis, resurrecting the specter of the worst days of sectarian fighting.

"If you had thought about a month without a death back during the surge in 2007 it would have been pretty hard to imagine because we were losing soldiers every day, dozens a week," said Col. Douglas Crissman, who is in charge of U.S. forces in four provinces of southern Iraq and oversaw a battalion in Anbar province during the troop increase, or surge. "I think this shows how far the Iraqi security forces have come."

None of the roughly 48,000 troops in Iraq were killed in August, a remarkable if fragile achievement, officials said. In all, 4,474 U.S. soldiers have died in the country since the U.S. invasion in 2003.

U.S. military commanders attribute the drop in deaths to the Iraqi government's finally pushing back against Iran and the Shiite militias, as well as aggressive unilateral strikes by U.S. forces. U.S. officials increased pressure on Iraqis to clamp down after the spate of attacks in June, and Iraq eventually responded. The government increased its counterterrorism operations against the militias, brought judges from Baghdad into the southern part of the country to ensure those captured were not summarily released and replaced poor-performing generals, officials said.