A private television station in the Afghan capital of Kabul was attacked on Tuesday by gunmen who entered the building after an explosion, a staff member who witnessed the attack said.

There was no immediate indication of casualties or the identity of the attackers.

"I saw three attackers on security cameras entering the TV station building. They first shot the guard and then entered the building. They started throwing grenades and firing," said Shamshad TV reporter Faisal Zaland, who escaped through a back door.

Shamshad TV, a Pashto language station that broadcasts nationwide, was transmitting a holding image instead of its normal programming.

Zaland told Agence France-Press that security forces were in the area of the Shamshad compound in the Afghan capital "trying to bring down the attackers".

"Many of my colleagues are still in the building," he added.