KABUL -- Four U.S. soldiers were killed in Afghanistan in three incidents Sunday, raising the total casualties this month to 33 international troops, including 21 Americans, NATO officials said.

Three of the soldiers were killed in insurgent attacks in the south and east, and one by a homemade bomb in the south, NATO officials said. The Taliban has stepped up its campaign of violence in those regions to counter a buildup of international forces.

NATO offered no other details of the deaths, citing procedures for notifying family members.

The number of U.S. troops killed this month is on a pace well below July's 66, which marked a monthly high in the nine-year war. That month had surpassed the previous high of 60 in June.

With the arrival of 30,000 additional U.S. forces this summer for a fall push into Taliban-controlled areas, NATO officials have predicted an increase in violence and casualties. The estimated 30,000 Taliban forces have spread beyond their traditional strongholds in the south and east to the once-peaceful north.

As the Taliban increases its attacks on troops, it has also killed a record number of civilians, through targeted assassinations, roadside bombs and suicide attacks. The insurgents' methods have grown more gruesome, including a reported stoning death of a young married couple this month -- the first such execution since the Taliban regime was toppled in 2001.

Also Sunday, NATO forces in Kandahar captured a Taliban commander who had been involved in ambushes, planting explosive devices and acquiring weapons.