Baghdad ? At least 447 Iraqi civilians were killed in June, double the toll from the previous month, according to an Associated Press tally, as insurgents took aim at crowded areas to maximize the number of casualties.

The spike in violence reflects the stiff challenges facing Iraqi security forces following the withdrawal of U.S. combat troops from urban areas this week. But the numbers are still far lower than previous years, and the bombings by suspected Sunni extremists are not triggering the type of retaliatory attacks from Shiite militias that nearly led to civil war in 2006-2007.

The number of American troop deaths, meanwhile, dropped to 15 in June after an eight-month high of 25 in May. Four U.S. soldiers were killed Monday — the last day of regular combat operations in the cities.

The high Iraqi toll was fueled by several huge bombings over the past 10 days, including the deadliest blast this year in a Shiite town near Kirkuk in northern Iraq. At least 82 people were killed in the June 20 attack.