A suicide car bomb has killed three NATO soldiers, including two Danes, an interpreter and three Afghan civilians in southern Afghanistan, officials say.

The Taliban have threatened to step up their campaign of suicide attacks this year to wear down Afghan and Western public support for the presence of foreign troops in the country.

The bomber attacked a convoy from the NATO-led International Security Assistance Force (ISAF) near the village of Girishk in the southern province of Helmand, an ISAF spokesman said.

"Three ISAF soldiers, one ISAF interpreter and three Afghan civilians were killed by the blast," said spokesman Captain Mark Gough. "Four ISAF soldiers and approximately six Afghan civilians were wounded."

Two Danish soldiers were killed and another wounded in the attack, the Danish Army Central Command said. The troops were working on a reconstruction project when they were attacked.

It was not immediately clear which country the third dead soldier was from, as ISAF does not release the nationalities of its casualties. Most foreign troops in Helmand are British, but another military spokesman said no British forces were there at the time. US and Estonian troops are also in Helmand.

Violence has spiralled since the hardline Islamist Taliban relaunched their insurgency to topple the pro-Western Afghan government and eject foreign troops two years ago.

The Taliban rely heavily on suicide and roadside bomb attacks, but as foreign forces use more heavily armed vehicles and are becoming better at avoiding casualties, a greater proportion of the victims are Afghan civilians.

The Taliban carried out more than 140 suicide attacks last year, killing some 200 civilians.

More than 12,000 people, including some 350 foreign soldiers, have been killed since 2006 in Afghanistan, according to United Nations estimates.

On Sunday night, a Canadian soldier was killed by an explosion in Kandahar, ISAF said.