HEART - Taliban have killed 15 police on a key highway in western Afghanistan, officials said Thursday, the latest in a growing number of rebel attacks as NATO-led troops withdraw.

"Highway One" is Afghanistan's main national road, connecting the cities of Kabul, Kandahar, Herat and Mazar-i-Sharif, but it has been a constant target of insurgent attacks, kidnappings and looting.

"A convoy of police who went to inspect a highway patrol unit were caught in a Taliban ambush on Wednesday," Farah province spokesman Abdul Rahman Zhuwandi told AFP.

"There was fighting between them in which 15 national police were killed and 10 wounded, while several Taliban were also killed."

The Taliban claimed responsibility for the attack shortly before dusk in Farah province's ethnically Pashtun district of Bakwa. The ambush raised the death toll from Taliban strikes on Wednesday to more than 30, including a US soldier, four policemen and three civilians who died when insurgents tried to storm a NATO-Afghan base in the eastern city of Ghazni.

Foreign troops are gradually withdrawing from Afghanistan as local security forces take over responsibility for battling the Taliban, who have launched a spate of recent attacks across the south, east and west.

Afghan and international leaders are trying to open peace negotiations with the militants before a presidential election in April and the departure of all 87,000 NATO combat troops by the end of 2014. In Wednesday's attack in Ghazni, about ten insurgents attacked a base that houses the provincial reconstruction team, one of the units that deploys foreign military and civilian staff to help development projects.

After a suicide bomb was detonated at the entrance, some insurgents managed to enter the base before being shot. Ten Polish soldiers were wounded.

Also on Wednesday, another Taliban strike on Highway One in Farah killed four drivers and set ablaze 40 trucks carrying NATO fuel supplies when a rocket was fired at a parking lot.

A suicide bomber rammed his explosives-laden car into a convoy of NATO troops in Helmand, killing four civilians.

The latest killings came after President Hamid Karzai, on a two-day trip to Pakistan earlier this week, called on Islamabad to help set up talks to end 12 years of war against the Taliban in Afghanistan.

Sections of the Pakistani state have been widely accused of funding and controlling the Islamist rebels for years, and many Islamist militant fighters live in Pakistan close to the Afghanistan border.

But Pakistan, which backed the Taliban's 1996-2001 rule of Kabul, denies the allegations and says it will work to stop the war in Afghanistan.

The Taliban regularly target foreign and Afghan soldiers, police and government employees in their guerrilla war against Karzai's Western-backed government.

Five Afghan aid workers and an government employee were killed on Monday in Herat province, and six truck drivers were found dead in the eastern province of Paktia two weeks after being kidnapped.