This story was updated at 10:45 pm EDT.

An explosion hit a minibus in the Afghan capital, Kabul, early on Monday, killing and wounding several people, police said, although it was not immediately clear who was on board the bus.

A Reuters witness saw several apparently dead victims and at least two wounded being carried out of the vehicle while police and emergency service vehicles rushed to the scene.

There was some uncertainty about the identity of the victims. One police official at the scene said the yellow bus had been carrying government employees to their offices in the city. However, another said the passengers may have been Nepalese security contractors.

There was no immediate word on the cause of the blast, which occurred during Ramadan, Islam's holy month.

Kabul An aerial view of Kabul, Afghanistan, Feb. 11, 2016. Photo: REUTERS/Ahmad Masood

It underlined how serious the security threat facing Afghanistan remains since the death of former Taliban leader Mullah Akhtar Mansour in a U.S. drone strike last month.

The blast follows a deadly suicide attack on a bus carrying justice ministry staff near Kabul last month and a separate attack on a court in the central city of Ghazni on June 1.

The Taliban claimed both those attacks in revenge for the execution of six Taliban prisoners.