The political office of the Afghan president’s running mate was hit by a large explosion and stormed by several gunmen who remained holed up inside, Afghan officials said Sunday.

The attack in the capital, Kabul, killed at least two people and came on the first day of campaigning for presidential elections, scheduled for late September.

Vice-presidential candidate and former intelligence chief Amrullah Saleh was “evacuated from the building and moved to a safe location,” said Nasrat Rahimi, the interior ministry spokesperson.

He said at least two gunmen could still be trapped in the top floor of the four-storey building, exchanging fire with security forces. Three attackers had been killed so far, he said, and some 75 people rescued from inside.

President Ashraf Ghani also tweeted that Saleh was unharmed during the “complex attack” targeting the Green Trend party headquarters.

At least two people, including a woman, were killed and 25 wounded, according to Wahidullah Mayar, the health ministry spokesperson.

Ferdous Faramarz, the spokesperson for Kabul’s police chief, said the explosion was likely a suicide car bomb.

The blast was large enough to be heard throughout the capital.

An Afghan family leaves the site of the deadly attack. Nasrat Rahimi, the interior ministry spokesperson, said vice-presidential candidate and former intelligence chief Amrullah Saleh survived. (Rahmat Gul/The Associated Press)

No one immediately claimed responsibility for the attack, but both Taliban insurgents and the Islamic State group are active in the capital and have carried out attacks there in the past.

Ghani is seeking a second term on promises of ending the 18-year war but has been largely sidelined over the past year as the U.S. has negotiated directly with the Taliban, who view the Kabul government as an American puppet.

The Taliban effectively control around half the country and have continued to carry out daily attacks on Afghan security forces.

Earlier Sunday, a Taliban suicide bomber killed four police officers in an attack on a police station in the eastern Ghazni province, according to Ahmad Khan Serat, a spokesperson for the provincial police.

U.S. envoy Zalmay Khalilzad, who is currently visiting Kabul, has held several rounds of talks with the Taliban in recent months in a bid to end America’s longest war. The two sides appear to be closing in on an agreement in which the U.S. would withdraw its forces in return for a pledge from the Taliban to keep the country from being used as a launch pad for global attacks.

The Taliban and the Islamic State group’s affiliate in Afghanistan are sharply divided over ideology and tactics, with the Taliban largely confining their attacks to government targets and Afghan and international security forces.

The Taliban and IS have fought each other on a number of occasions, and the Taliban are still the larger and more imposing force.