Attackers struck a US-run civilian-military base in the southern Afghan city of Kandahar on Thursday, where explosions and gunfire could be heard, police and witnesses said.

"The attack is continuing on Kandahar PRT (provincial reconstruction team) from different directions," said the city's police spokesman Ghorzang, who like many Afghans goes by only one name.

He said five explosions had been heard at the base, but it was not immediately clear if they were caused by the attackers, or by the PRT guards to defend the base.

The road leading to the base had been blocked, but one witness who owns a nearby shop said he had also heard sporadic gunfire.

"The armed men have taken position in a building near the PRT base and are firing on the base," said shop owner Abdullah.

The Taliban claimed responsibility for the attack and said the gunmen were armed with suicide vests.

"A group of our men have attacked Kandahar PRT base, as well as an NDS (Afghan intelligence) office nearby. Our men are very well armed, they are suicide attackers," said spokesman Yusuf Ahmadi.

The Taliban militia, which is leading a 10-year insurgency against US-led NATO troops, has increasingly carried out coordinated attacks on high-profile Western and government targets.