KABUL, Afghanistan (AP) — Three separate explosions in the Afghan capital Kabul on Saturday killed at least five people and wounded two others, a police official said, amid a surge in violence in the war-torn country.

Kabul police spokesman Ferdaws Faramarz said the first two explosions took place 15 minutes apart and a third targeting a police vehicle took place two hours later.

No group immediately claimed responsibility.

It wasn't immediately clear what caused the blasts. The majority of bomb attacks in the capital Kabul in recent months have been sticky bombs — explosive devices with magnets that are attached to vehicles and detonated by remote control or timer.

The second explosion targeted a car in a northwestern Kabul neighborhood in which national army soldiers were traveling, killing two soldiers. A civilian passerby was also killed.

The third explosion destroyed a police car in western Kabul killing two police officers. Meanwhile, the first blast targeted a civilian car wounding both travelers inside the vehicle.

Kabul police said investigations were underway.

Afghanistan has seen a nationwide spike in bombings, targeted killings and violence on the battlefield as peace negotiations in Qatar between the Taliban and the Afghan government have stalled.

The Islamic State group’s local affiliate has claimed responsibility for some of the attacks, but many go unclaimed, with the government putting the blame on the Taliban. The insurgents have denied responsibility for most of the attacks.