Taliban insurgents set fire to about 200 oil tanker trucks supplying fuel for NATO forces in an attack just outside the Afghan capital Kabul, police said.

Black smoke was seen billowing above the site of the attack, with the charred wreckage of dozens of trucks scattered around a vast parking area.

The Taliban claimed responsibility for the attack, saying the trucks carried fuel intended for US-led NATO forces.

It was unclear how the fire was started.

Some Afghan media reported that insurgents had fired rockets at the tankers last night.

There were no immediate reports of casualties.

"The number of tankers on fire is not yet clear, but based on preliminary reports from police around 200 tankers have been burnt," the interior ministry said in a statement.

The attack happened as Afghanistan prepares to announce preliminary results of the final round of a presidential election on Monday in a tense atmosphere.

Each of the two candidates vying to succeed President Hamid Karzai accuses the other of mass fraud.

The Taliban have vowed to disrupt the election process.

On Thursday, militants fired rockets into Kabul's international airport, destroying a helicopter.