A Taliban suicide bombing has killed at least six soldiers, including three members of the NATO force ISAF, and wounded more than 25 others near the US embassy in Kabul, according to police sources in Afghanistan's capital.

The car bomber attacked a military convoy just a couple of hundred yards from the embassy compound at about 8am (0330 GMT) on Tuesday, causing a huge blast that rattled the neighbourhood, the police said.

Faird Afzalai, chief of criminal investigations for Kabul's police, confirmed reports that the bomber targeted a foreign convoy. Three of the victims were Afghan soldiers.

The blast happened near the country's Supreme Court on a busy road that runs from the heavily fortified US embassy to Kabul airport.

In the aftermath of the explosion, which occurred during heavy rush-hour traffic, Afghan and foreign troops secured the area as fire and rescue vehicles moved in.

At the side of the road, foreign troops gave first-aid to some blood-stained fellow soldiers from the convoy.

About a half dozen cars stood damaged, and investigators inspected an empty black 4WD vehicle, its windows smashed and exterior pockmarked with shrapnel.

One vehicle from the convoy was thrown off the road and destroyed by the blast.

The Taliban claimed responsibility for the attack in an emailed statement to journalists and via a recognised Twitter account.

A Polish military spokesman later said one Polish soldier was killed and two others were wounded but were not in danger. Lieutenant-Colonel Piotr Walatek identified the dead soldier as Sergeant Rafal Celebudzki, who was driving one of the convoy's vehicles.

Political deadlock

The attack in Kabul comes as the country's two presidential contenders continue negotiations to form some sort of national unity government.

The candidates on Monday held talks on ending the deadlock over who won the election to replace President Hamid Karzai, who has ruled since the fall of the Taliban.

Ashraf Ghani and Abdullah Abdullah have been arguing over a power-sharing deal after the vote was engulfed in allegations of fraud that have threatened to cause instability as US-led NATO troops of ISAF pull out of the country.

Ghani, who is widely tipped to emerge as the new president, won the run-off election according to preliminary results, but Abdullah has consistently said he was the victim of state-backed ballot-rigging.

Aimal Faizi, spokesman for Karzai, declined to give details of the agreement, which both campaign teams have previously said would hinge on the power held by a new chief executive officer (CEO), who would be nominated by the election loser.

"We are in the middle of a political crisis here," Al Jazeera's Jennifer Glasse, reporting from Kabul on Tuesday, said.

"It's very tense here, and we have a population that is waiting who will be the next president."

She said that with the explosion, questions would be raised about how a car loaded with explosive got close to a "very secure part" of Kabul.

With the government paralysed for months, it has also emboldened the Taliban, weakened the fragile economy and put future international military and aid support at risk.

The UN has expressed fears that the dispute over the poll results could revive the ethnic violence of the 1990s civil war, when nationwide chaos allowed the Taliban to come to power.