KANDAHAR, Afghanistan (AFP) - Taleban insurgents have launched a prolonged attack on a major Afghan army base that was handed over by NATO forces last month, officials said Friday, in another sign the militants are on the offensive as foreign troops leave.

Camp Bastion, now know as Shorabak, was Britain's biggest military base in Helmand province and was a key airfield for US-led NATO operations in the Taleban heartlands of southern Afghanistan.

The attack started on Thursday evening and continued on Friday, the Afghan military said.

Thursday also saw a Taleban attack on a foreign guesthouse in Kabul and a suicide bomber target a British embassy vehicle in a blast that killed six people.

"Last night a group of enemy fighters tried to storm Shorabak camp. One detonated a suicide car bomb at the gate and others tried to enter," Ghulam Farooq Parwani, a senior Afghan army commander at the camp, told AFP.

"In the fighting overnight, there were more suicide attacks and 20 other militants were killed.

"Two injured militants have been cornered and will be hunted down." Parwani said five Afghan soldiers had died, but dismissed Taleban claims that a far larger number of soldiers had been killed or aircraft and tanks had been destroyed.

Also on Friday, a suicide attack elsewhere in Helmand killed four people in Nawzad district, and a blast in a mosque in the eastern province of Nangarhar injured 26 people.

The 13-year NATO combat mission finishes at the end of this year, to be replaced by a 12,500-personnel follow-up mission to support the Afghan army and police who are now responsible for defeating the Taliban.

NATO troop numbers in Afghanistan peaked at 130,000 in 2010, and fears are growing that the declining international presence will boost the extremist insurgency.