According to Karzai’s office, troops broke into the house of Haji Ibrahim, a former district governor in the southern province of Helmand, earlier this week, killing him and arresting six members of his family.

Gulab Mangal, the Helmand governor, told Karzai preliminary investigations had revealed Ibrahim was innocent, the president’s office said in a statement.

Six members of Ibrahim’s family who also “appeared to be innocent” were detained, the statement said.

Karzai had ordered Mangal to open an investigation into the killing, the statement added.

Daud Ahmadi, a spokesman for the Helmand provincial administration, said an investigation was already under way.

“The governor has written to the NATO forces inquiring the reason behind the killing. But so far, they have not written back,” Ahmadi said.

The US-led NATO force, currently numbering around 150,000 and based in Afghanistan to defeat a Taleban-led insurgency is usually accused of killing civilians during operations against militants.

Meanwhile, three NATO service members have been killed by bombs and insurgent fighting in the south and east, both areas that have seen heavy fighting since 30,000 American reinforcements arrived, NATO said Thursday.

One service member was killed by insurgents Thursday in the south and another died in a roadside bomb blast in the east. A third service member was killed Wednesday, also in a roadside explosion, in the south.

The military coalition did not release details of the deaths, or disclose the nationalities of the service members killed.

They are the first three NATO troops killed so far this month; 55 died in November.

Also on Thursday, Afghan and coalition forces detained numerous suspected insurgents during two security operations in the south and east.

On Wednesday, militants seized 16 Afghan demining experts in Nangarhar province near the Torkham border crossing into Pakistan.

They released nine of the deminers hours after the ambush, but were still holding the seven others, Fazel Wahab, from OMAR, an Afghan humanitarian group working to find and dismantle homemade bombs, said Thursday.