A suicide bomber blew himself up at the Afghan interior ministry Wednesday, killing six police officers just three days before the country’s presidential election, which the Taliban have vowed to disrupt.

A suicide bomber blew himself up at the Afghan interior ministry Wednesday, killing six police officers just three days before the country's presidential election, which the Taliban have vowed to disrupt.

The attack came as the three leading candidates to succeed President Hamid Karzai made a final push for votes with rallies on the last day of campaigning.

Kabul has been rocked by a string of high-profile attacks in the run-up to Saturday's US-backed election, which will be the first democratic handover of power in Afghanistan's turbulent history.

"The suicide attacker wearing a military uniform detonated himself near the gate of the ministry killing six policeman," interior ministry spokesman Sediq Sediqqi told AFP.

He said that the blast occurred in an annex to the ministry, which is one of the most closely-guarded buildings in the Afghan capital.

"We heard a huge bang from the interior ministry and we were ordered to our (reinforced) safe room," an Indian diplomat who was working next door to the ministry told AFP on condition of anonymity.

The election is seen as a benchmark of progress since the Taliban were ousted from power in 2001, and the militants have urged their fighters to target polling staff, voters and security forces.

On Saturday, the Kabul headquarters of the Independent Election Commission (IEC) was attacked when five Taliban militants occupied a nearby building and unleashed rockets and gunfire at the fortified compound.

All five attackers were killed by Afghan security forces six hours after the attack began, and there were no other casualties.

Another IEC centre, Kabul's most prestigious hotel and a guesthouse run by a US anti-landmine charity have also been targeted in recent weeks.

Former World Bank economist Ashraf Ghani, Abdullah Abdullah, runner-up in 2009, and former foreign minister Zalmai Rassoul are the leading contenders in the eight-man race.

A repeat of the bloodshed that marred the 2004 and 2009 elections would damage claims by international donors that the multi-billion-dollar 13-year intervention in Afghanistan has made progress in establishing a functioning state system.

The Afghan government has pledged to ensure a safe election, with police and soldiers providing security for the vote, though the NATO military coalition has said it will assist if necessary.

Whoever wins the race to succeed Karzai faces a testing time maintaining stability as Afghan forces take on the fight against the resilient Taliban insurgency without the aid of NATO forces.

The US-led coalition is due to withdraw its 53,000 combat troops from Afghanistan by the end of the year.