A twin suicide bomb attack targeted a Nato base in eastern Afghanistan, killing eight civilians and four Afghan policemen, local officials said.

A spokesman for Nato's International Security Assistance Force (ISAF) said no one from the alliance was killed in the attack, which happened in Wardak province's Sayed Abad district.

"The truck bomb was huge, killing 12 and wounding 50 more," said provincial governor spokesman Sahidullah Shahid.

The Taliban, which took responsibility for the early morning attack, said it had dispatched two bombers, one on foot and one in an explosives-laden truck.

The Nato base was targeted last year on the eve of the 10th anniversary of the September 11 attacks when a suicide bomber drove into it, killing four civilians and wounding 77 US troops.

Wardak province saw the worst single incident suffered by foreign forces in over 10 years of war when the Taleban shot down a transport helicopter last year, killing 38 troops, 30 of whom were American, mostly elite Navy SEALs.

Two US troops were killed on Saturday in a separate insurgent attack in eastern Ghazni province, ISAF said in a statement.

Violence is increasing across Afghanistan ahead of the 2014 deadline for Nato to withdraw most of its troops, and fears are mounting that the 350,000-strong Nato-trained Afghan security forces will not be able to tackle insurgents once they leave.

This week 19 Afghans, including an adolescent boy and a young girl, were beheaded in three separate attacks.

Insider attacks, when Afghan forces turn their weapons on foreign troops, have sharply shot up.

Three Australian soldiers were shot dead by a gunman wearing an Afghan army uniform this week, bringing to 15 the number of foreign soldiers killed this month in insider attacks.

A total of 45 Nato-led coalition troops have been killed in rogue shootings this year.

- Reuters