KABUL, Afghanistan — Foreign intelligence agents are leading secret, deadly raids on suspected insurgents in Afghanistan and shirking responsibility when innocent civilians are killed, a U.N. official alleged Thursday.

Philip Alston, a special investigator for the U.N. Human Rights Council, referred to three such recent raids in the country’s south and east.

While he didn’t specifically mention any intelligence agencies, he appeared to imply American involvement. U.S. military officials declined to comment on the allegations.

Alston said the raids were part of a wider problem of unlawful killings of civilians and lack of accountability in Afghanistan. He said about 500 civilians had been killed this year, most of them at the hands of the Taliban but some by Afghan police.

NATO and the U.S.-led coalition have nearly 70,000 soldiers fighting the Taliban-led insurgency in Afghanistan and say they make every effort to prevent civilian casualties.

On Thursday, a suicide bomber wearing a burqa attacked police at a crowded market in the western province of Farah. Along with the 12 people killed, 27 were wounded.

The provincial government said the bomber was a woman. The Taliban, who claimed responsibility for the attack, said the bomber was a man.