Gunmen stormed a television station in Kabul on Tuesday and many staff were still in the building, an employee told AFP, describing the attack as ongoing.
"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 AFP 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.
Taliban spokesman Zabiullah Mujahid denied the militant group was involved in the attack in a Twitter post.
The interior ministry told AFP it was investigating the incident but had no further details.
Kabul has been rocked by a series of deadly attacks in recent weeks as the Taliban and Islamic State insurgents step up offensives against security installations and mosques.
Last Tuesday a suicide bomber, believed to have been as young as 12 years, struck Kabul's heavily fortified diplomatic quarter and killed at least five people, showing that militants can still hit the heart of the city despite tighter security.
Security in Kabul has been ramped up since a May 31 truck bomb went off on the edge of the so-called "Green Zone", killing around 150 people and wounding 400 others.
Special truck scanners, barriers and permanent and mobile checkpoints have been rolled out across the city.
The last major assault in Kabul was on October 21 when a suicide attacker hit a busload of Afghan army trainees, killing 15.
On October 20 a suicide bomber pretending to be a worshipper blew himself up inside a Shiite mosque in the city during evening prayers, killing 56 and wounding 55.
Earlier this month Kabul police stopped a lorry carrying 2,700 kilogrammes of explosives hidden under boxes of tomatoes, averting a potentially deadly blast.