KABUL: A fierce gunfight backed by US helicopter fire paralysed a district in eastern Afghanistan after Taliban forced their way into a clinic seeking treatment for their leader, officials and NATO said Thursday.

An American soldier was killed in the violence, which broke out Wednesday as Afghan forces were trying to capture a suspected Taliban commander, the International Security Assistance Force (ISAF) under NATO said.

Twelve Taliban were killed in the fighting that raged for about six hours, and six others were captured, said Hamidullah Zhwak, the provincial spokesman, adding a clinic guard was also wounded.

Acting on a tip-off, Afghan security forces surrounded the clinic at around midday in the small Sar Hawza district of Paktika province, which borders Pakistan and is a hotbed of Taliban violence.

The ISAF statement said the "suspected insurgent leader" was being treated for injuries suffered during fighting on election day, August 20.

The Afghan soldiers "were clearing the clinic when they received direct fire attack," the statement said.

More troops, international and Afghan, arrived to provide backup, it said, and once all civilians had been brought safely out of the clinic, an Apache helicopter was called in to fire on the building.

The helicopter strafing ended the "the direct threat," ISAF said, "injuring the targeted insurgent in the building."

No civilians were killed, ISAF said.

"This clearly shows the disparity between coalition forces and anti-Afghan forces when it comes to concerns for civilians caught in the crossfire," said Major Matthew Gregory, a spokesman for ISAF.

In the neighbouring province of Khost, a roadside bomb killed four border police and wounded three others on Thursday in Gurbuz district, said police official Sher Ahmad Kochai, blaming the Taliban for the attack.

The Taliban have widening influence in eastern and southern Afghanistan and have been particularly active around the election, only the second in Afghanistan's history to choose a president.

In early counting, President Hamid Karzai is leading his main rival, former foreign minister Abdullah Abdullah 42.3 percent to 33.1 percent.

The campaign to instill enough fear in people to deter them from voting appears to have had a serious impact, as figures extrapolated from early results suggest 30-35 percent of registered voters turned out.

Violence peaked on election day, with reports from a variety of sources of rocket, grenade and suicide attacks, gunfights and afterwards beatings and even finger amputations of people who voted.

The Taliban have also stepped up their attacks on foreign soldiers -- who under NATO and US command number more than 100,000 -- in Afghanistan to wipe out the insurgency.

The Taliban's weapon of choice is the improvised explosive device, or IED, usually a concealed roadside bomb detonated remotely and, increasingly, linked to others to cause maximum damage, often killing civilians.

ISAF said Thursday an American soldier was killed in southern Afghanistan when his patrol was struck by an IED and then ambushed by insurgents.

"The patrol responded to the attack but a service member was killed in the engagement," an ISAF statement said.

After only nine months, 2009 has become the deadliest year for foreign troops in Afghanistan since the 2001 US-led invasion.