Eight NATO troops were killed in southern Afghanistan in a 24-hour period ending Friday, Western military officials said.

NATO’s International Security Assistance Force did not disclose the nationalities of the troops, but most of those serving in southern Afghanistan are American or British. The south of Afghanistan includes the volatile provinces of Helmand and Kandahar, the traditional heartland of the Taliban.

Four of the eight were killed Friday in a single explosion, military officials said in a statement, and a fifth died as the result of an earlier “insurgent attack,” a phrase often used to characterize a firefight with Taliban militants.

Late Thursday, military officials announced that three troops were killed in the south by a makeshift bomb. Such crude but powerful bombs remain the largest single killer of Western troops in Afghanistan.

U.S. troop fatalities fell in 2011 for the first time in four years, and overall NATO deaths dropped as well. About 10,000 U.S. troops left Afghanistan in the latter part of last year, and 23,000 more are scheduled to depart by the end of this year.

U.S. commanders have said they expect the military focus this year to shift to eastern Afghanistan, bordering Pakistan’s tribal areas. The Haqqani network, considered the most dangerous insurgent group, operates mainly in the east.

But the south, which was the scene of major U.S.-led offensives during the past two years, shows signs that it has not been pacified. Local officials say that insurgents have filtered in to retake ground that had been gained by Western troops and that poppy cultivation and trafficking — a major revenue source for the Taliban and other militant groups — appear to be on the rise again.

Also Friday, explosives hidden in a trash heap killed six children in southern Afghanistan, the Associated Press reported, citing police accounts.

The children were rummaging through the trash for food scraps and bottles in Tarin Kot, the capital of Uruzgan province, northwest of Kandahar, when the blast killed them, police said.

Four other children were injured in the blast, and a civilian man also died.

— Los Angeles Times