Eleven members of an Afghan family were killed on Friday when their vehicle hit a roadside bomb while they were travelling to an engagement ceremony in the country's volatile east.

Five women, five children and a man in a vehicle were killed and one woman and two men were wounded in the blast in Logar province, just south of the capital of Kabul, said Mohammad Halim Fedayee, the provincial governor.

"The bomb struck their Toyota sedan when they were going for an engagement ceremony," said Fedayee.

No group has so far claimed responsibility but provincial authorities blamed the Taliban, who launched their annual "spring offensive" last month, for the killings.

Roadside bombs have been the Taliban's weapon of choice in their war against foreign and Afghan security forces.

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The first four months of 2017 saw the highest recorded number of child casualties from the conflict in Afghanistan, the United Nations reported on Monday, with at least 283 killed and 704 wounded as of the end of April.

Last year, at least 3,498 civilians were killed and 7,920 were wounded, a combined increase of 3 percent over 2015, according to a UN report released in February.

The UN Assistance Mission in Afghanistan voiced alarm when five boys from one family were killed earlier this month by an unexploded mortar round in Laghman.

Elsewhere in Afghanistan, another roadside bomb targeted a US militarily convoy in northern Parwan province on Friday, the international mission's media officer, Doug High, said.

The explosion disabled an armored vehicle but caused no injuries, High said. After recovering the vehicle, the convoy continued on its mission, he added.

Afghan policeman kills 5 colleagues

Meanwhile, on Thursday night an Afghan policeman turned his rifle on his colleagues as they slept at an outpost in eastern Nangarhar province, killing five.

In the Thursday night attack, district governor, Abdul Wahab Momand, said the policeman shot his colleagues at an outpost in the district of Ghanikhil.

After the shooting, the attacker, who was only identified by one name, Nasratullah, seized all the victims' firearms and fled the scene, the governor said.

Neither the Taliban nor the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) - the two armed groups who operate in the area - immediately claimed responsibility for the attack in Nangarhar, a mountainous province that borders Pakistan.