KANDAHAR, Afghanistan - Taliban militants have rejected a peace overture from President Hamid Karzai, saying Monday there would be no negotiations until foreign troops leave Afghanistan.

Karzai offered Sunday to provide security for reclusive Taliban leader Mullah Omar if he enters negotiations and said the U.S. and other western countries could leave Afghanistan or oust him if they disagree.

But Zabiullah Mujahid, a Taliban spokesman, said there could be no talks while foreign troops are in the country.

"The Taliban's (leadership) decided they will not take part in any peace talks with Karzai or Karzai's administration until such a day when foreign forces leave Afghanistan," Mujahid told the Associated Press.

"The Taliban will pursue jihad against foreign forces and (Karzai's) government," he said, while speaking from an undisclosed location.

In Washington, State Department spokesman Sean McCormack questioned Karzai's security guarantee.

"One can't imagine the circumstances where you have the senior leadership of the Taliban -- that there would be any safe passage with respect to U.S. forces. Certainly, it's hard to imagine those circumstances standing here right now," McCormack said.

Karzai has dismissed the demand for foreign troops to leave, saying they are needed to keep Afghanistan safe.

The Afghan president has long supported drawing the militia into the political mainstream if they accept the country's constitution and repudiate al-Qaida.

But his repeated offers to talk could also be aimed at portraying the insurgents as bent on violence instead of potentially legitimate rulers.

U.S. political and military leaders are also considering negotiating with some elements of the Taliban as the insurgency gains sway in large areas of Afghanistan, especially its south and east.

Afghanistan is going through its worst violence since the 2001 U.S.-led invasion ousted the Taliban government in 2001.

In the past, no senior Taliban leader has publicly indicated the hardline movement is willing to enter serious talks with what they call Karzai's "puppet government."

Mujahid said the peace overtures are a political ploy by Karzai ahead of next year's planned presidential elections.

"Why did he not ask for these negotiations seven years ago?" Mujahid said. "Now it is useless to ask for peace negotiations. It is just part of his election campaign."

Meanwhile, a roadside bomb aimed at Afghan soldiers in southern Afghanistan killed four civilians, while a suicide bomb attack in the same region killed three other people, an official said.

Monday's roadside attack on the Afghan army patrol lightly damaged their vehicle, and instead hit a nearby group of civilians in Kandahar province's Panjwai district, said Zalmai Ayubi, the provincial governor's spokesman.

Four civilians were killed and eight others were wounded in the explosion, Ayubi said. He accused the Taliban of planting the bomb.

Southern Afghanistan is the centre of the Taliban-led insurgency, in which attacks have risen 30 per cent since 2007.

Separately, two police officers and a civilian died when a suicide bomber blew himself up at the entrance of a government office in Kandahar's Dand district, Ayubi said.

Three other officers were wounded when they tried to stop the bomber from entering the offices of the district chief, he said.

In eastern Afghanistan, meanwhile, Afghan troops repelled a Taliban attack on another district centre in Nangarhar province Sunday, killing three militants, said police spokesman Ghafoor Khan.