KABUL, Afghanistan (AP) — Attackers threw a pair of grenades at the gate of a military training center in Kabul on Monday, wounding at least four Afghan soldiers and a civilian, an official said.

Interior Ministry spokesman Nasrat Rahimi initially said the back-to-back explosions were caused by suicide bombers but later said that it was from a pair of hand grenades.

No one immediately claimed responsibility for the attack.

The grenades were hurled at the entrance of the Military Training Center on the western edge of Kabul at around 7:30 a.m. as recruits were arriving for classes and training.

Both the Taliban and the Islamic State group regularly target Afghan security forces and government officials in Kabul and elsewhere across the country. Monday’s attack came just days after a suicide car bomb targeting a security firm in Kabul killed 12 people, including several children on their way to school.

Afghan President Ashraf Ghani had last week announced the conditional release of three prominent Taliban prisoners but later had them returned to custody, saying their release was being reconsidered.

The three were to be exchanged for two professors of the American University in Kabul — an American, Kevin King, and an Australian national, Timothy Weeks. The two were abducted by the Taliban in 2016.

One of the three Taliban prisoners to have been released was Anas Haqqani, the younger brother of the Taliban deputy head Sirajuddin Haqqani, who also leads the fearsome Haqqani network.