At least five civilians have been killed in a bomb blast outside a Kabul mosque, a Taliban official said.

It was the deadliest attack in the Afghan capital since US forces left at the end of August

Taliban spokesman for the interior, Qari Saeed Khosti, confirmed the deaths. Initial reports indicate the explosion was caused by a roadside bomb. Three suspects have been arrested, Bilal Karimi, Taliban official spokesman said.

The bomb targeted the sprawling Eid Gah Mosque, where a memorial service was being held for the mother of Taliban spokesman Zabihullah Mujahid. He later tweeted the attack had claimed civilian lives.

Taliban fighters were not harmed in the attack, Taliban spokesman Bilal Karimi told the Associated Press. Those killed in the attack were civilians standing outside the mosque gate.

An Italian-funded emergency hospital in Kabul tweeted it had received four people wounded in the blast.

Following the blast, the area around the mosque was cordoned off by the Taliban, who maintained a heavy security presence. Later in the afternoon, the site was cleaned. The only signs of the blast was slight damage to the ornamental arch by the entrance gate.

No one immediately claimed responsibility for the attack. However, since the Taliban takeover of Afghanistan in mid-August, attacks by so-called Islamic State group militants against them have increased. The rise has raised the possibility of a wider conflict between the two extremist groups.

IS maintains a strong presence in the eastern province of Nangarhar and considers the Taliban an enemy. IS has claimed several attacks against the Taliban, including several killings in the provincial capital of Jalalabad.

Sunday’s attack is the first to target the capital since late August when an IS suicide bomber targeted American evacuation efforts outside Kabul’s international airport. The blast killed 169 Afghans and 13 US service members and was of the deadliest attacks in the country in years.

It was claimed by an IS affiliate, the Islamic State in Khorasan Province.

Attacks in Kabul have so far been rare, but in recent weeks IS has shown signs it is expanding its footprint beyond the east and closer toward the capital.

On Friday, Taliban fighters raided an IS hideout just north of Kabul in Parwan province. The raid came after an IS roadside bomb wounded four Taliban fighters in the area.