A truck bomb exploded at a NATO military base south of the Afghan capital Tuesday, wounding three soldiers and at least 17 civilians, Afghan police said.

A spokesman for NATO's International Security Assistance Force confirmed that "there has been an explosion outside an ISAF facility in Logar province" and that a number of troops were wounded.

"We have information that ISAF members were wounded but it is our policy not to confirm the number or condition of the injured," he said, adding that the cause of the explosion was under investigation.

Provincial police chief Ghulam Sakhi Rogh Lewanai told AFP: "A truck loaded with explosives detonated at the coalition forces' camp in (provincial capital) Pule Alam city.

"So far we have information that 17 Afghan civilians and three ISAF soldiers have been injured," he said, updating an earlier toll of 12 hurt.

He said most of the civilians worked at the base. ISAF said the explosion was outside the base, near an Afghan bazaar.

Taliban insurgents claimed the attack, some 70 kilometres (40 miles) south of the capital Kabul.

"At around 9:00 am (0430 GMT) one of our mujahideen (holy warriors) carried out a suicide truck bomb attack on a big US forces' camp resulting in many deaths and injuries," Taliban spokesman Zabiullah Mujahid said in a text message.

Earlier Tuesday, a Taliban bomb killed eight people and wounded five when it struck a minibus on the western outskirts of Kabul, police said, amid growing unrest in areas neighbouring the Afghan capital.

Three Afghans who worked for NATO in Logar were kidnapped by the Taliban and their bodies dumped last week in the main bazaar of Charkh district, local officials said.

ISAF, which has 130,000 US-led troops in Afghanistan, has noted a spike in attacks countrywide in recent months, since the start of the insurgents' annual summer offensive.

June saw the highest number of attacks in nearly two years, with more than 100 assaults a day across the country, including firefights and roadside bombings, the coalition said.