Image copyright AFP/Getty Images Image caption A police spokesman said the eight men were drugged by a colleague before being killed

Eight policemen, all members of one family, have been shot dead in northern Afghanistan.

Government officials said the group were drugged and killed at a checkpoint in Faryab province.

Some reports claim their killer was a colleague who was secretly working with the Taliban, while one said he was a Taliban fighter who had surrendered.

The victims are said to be a father, two sons, two sons-in-law and three nephews.

No group said it had carried out the attack, but a spokesman for Faryab provincial police told AFP news agency the suspect had "fled back to the Taliban".

Abul Karim Yoresh told AFP the victims were four regular policemen and four auxiliary officers.

They "were drugged by their colleague, who then opened fire on them at a police checkpoint in the Almar district" of Faryab province, he said.

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District governor Saleh Saleh confirmed that all eight of the dead were members of the same family.

A similar incident saw two killed in the northern province of Kunduz in September, when two Afghan soldiers opened fire on their sleeping colleagues.

An official US report earlier this week said the number of Afghan security personnel killed last year rose by a third over the previous year's tally.