NATO troops in a convoy killed an Afghan cleric as he was driving on Thursday in Kabul, prompting a protest outside a U.S. military base.

Police and witnesses said imam Mohammad Yunus, 36, was shot to death with his young son in the vehicle as he approached a main road from a side street.

NATO said foreign forces opened fire on “what appeared to be a threatening vehicle,” killing the cleric who presided over services at the Paktia Kot mosque.

The cleric was hit by four bullets and died on the way to the Wazir Akbar Hospital, according to his son–in-law, Abdul Qadir, adding the family had taken the body to the province of Laghman for burial. Yunus had two wives and 10 children, Abdul-Qadir said.

A shopkeeper who witnessed the shooting said the convoy was composed of American armoured vehicles and was travelling on the main road in the direction of Jalalabad. A gunner in the first vehicle opened fire as Yunus began to pull onto the same road, the 25-year-old shopkeeper said, identifying himself only as Aymal.

Aymal said he didn’t hear any warnings before the gunfire. NATO said an investigation was under way and appropriate action would be taken to ensure that the troops complied with policies aimed at protecting civilians. It said Yunus’ family would be compensated in accordance with local customs.

Dozens of demonstrators gathered outside Camp Phoenix to protest the killing. They dispersed after police promised the Americans would discuss the death with local elders, according to Abdul Qadier and district police chief Col. Rohullah, who like many Afghans only uses one name.

A recent U.N. report showed that the number of civilians killed by NATO-led forces has dropped after U.S. Gen. Stanley McChrystal, the top NATO commander in Afghanistan, ordered measures curbing the use of airstrikes and other weapons to protect the population.

It said civilian deaths at the hands of the Taliban have increased.

“Despite all the measures that we put in place to ensure the safety of the Afghan people, regrettable incidents such as this one can occur,” NATO spokesman Brig. Gen. Eric Tremblay said in a statement about Thursday’s shooting. “On behalf of ISAF I express my sincere regrets for this loss of life and convey my deepest condolences to his family.”

In other violence on Thursday, a U.S. service member was killed by a roadside bomb in southern Afghanistan, according to the international force. The death brings to at least 26 the number of American deaths in Afghanistan this month, nearly double the 14 killed in all of January last year.

An Afghan policeman also was shot to death by two militants on a motorcycle in the southern city of Kandahar, provincial police chief Gen. Sardar Mohammad Zazai said.

NATO also confirmed that as many as 20 suspected militants were killed on Wednesday in fighting in northern Afghanistan.

Provincial police said on Wednesday that 11 insurgents, including two senior commanders, were killed in a joint air and ground assault targeting a Taliban compound west of Pul-e-Khumri, the capital of Baghlan province.

Joint forces called in air support after coming under fire from a large number of insurgents armed with rocket-propelled grenades, NATO said in a statement issued on Thursday. It said attack aircraft “bombed and strafed insurgents in a treeline,” killing 12 to 20 of them.

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