An explosion ripped through a school in southeastern Afghanistan (search), killing nine youngsters and one adult, the U.S. military said Sunday.

Paktia Gov. Asadullah Wafa said the blast Saturday night in Paktia province (search) was caused by a bomb planted by "puppets listening to their bosses outside the country."

He did not elaborate, but the remark appeared aimed at neighboring Pakistan, which many Afghans accuse of doing too little to prevent Taliban (search) militants from mounting cross-border attacks.

The U.S. military said the cause of the explosion was not clear.

"There was an explosion, that's all we know," American spokeswoman Master Sgt. Ann Bennett said. "Killed were four children, five teenagers and one adult."

An eight-year-old boy injured in the blast was taken to an American military base for treatment, Bennett said.

Wafa said eight children aged 7-15 were killed and 15 other people injured, three of them critically. It was not clear if two had subsequently died of their wounds.

The military initially reported that about 30 children and two adults were wounded. Bennett said the toll was revised after reports from U.S. medical teams sent to help.

The military said it was helping local authorities investigate the explosion, which Bennett said occurred as the children were attending an evening class.

The Mullah Khel school (search) near Zormat, 80 miles south of Kabul, was an Islamic school which also taught the more modern syllabus set by the Afghan Education Ministry.

It received funding from an international aid group, Wafa said, something that could conceivably have made it a target for Taliban-led militants.

Civilians have often been among the victims of relentless violence between rebels and Afghan and U.S. forces across the south and east of Afghanistan.

In one of the worst incidents, 13 children and two adults were killed Jan. 6 in southern Kandahar province by a time-bomb concealed in an apple cart on a street regularly used by U.S. military patrols.

A Kabul court has sentenced a suspected Taliban militant to death over that attack. The man has appealed.

American troops have also been involved in a string of botched operations that have killed dozens of civilians.

Most recently, U.S. soldiers shot dead three unarmed Afghans on Aug. 21 after their car did not stop at a checkpoint in Ghazni province. The military has apologized.