BAGHDAD — Under increased U.S. pressure, 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 most deadly 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, 4,465 U.S. soldiers have died here since the U.S. invasion in 2003, according to Defense Department figures.

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. If the Americans are correct, and August is not just a statistical blip, it may also be connected to the ongoing negotiations between U.S. and Iraqi officials over whether to leave some troops behind after the end of the year, experts said. Although all sides in Iraq have said they want the Americans to leave, each has some interest in seeing that some troops stay behind.