A Taliban suicide bomber blew himself up at the Afghan Interior Ministry Wednesday, killing six police officers just three days before the presidential election, which the insurgents 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 runup to Saturday’s 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 policemen,” 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.

A diplomat in the Indian Embassy, which is next door to the ministry, told AFP he heard a huge bang and that he and his colleagues were ordered to shelter in reinforced safe rooms.

The Taliban claimed responsibility for the attack through one of their recognized Twitter accounts.

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.

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

Another IEC center, Kabul’s most prestigious hotel and a guesthouse run by a U.S. 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 and fraud that marred the 2009 election would damage claims by international donors that the multibillion-dollar 13-year intervention in Afghanistan has made progress in establishing a functioning state system.