Two people were killed and three others wounded when an explosion and ensuing gunfire rocked a TV station in Kabul on Tuesday.At least four gunmen were involved in the attack at the Shamshad TV headquarters in Chaman-e-Huzuri neighbourhood in Police District 8 of the city, a security source told Xinhua news agency. Witnesses said the attackers, disguised in police uniforms, threw grenades and fired guns as they entered the building, the BBC reported. "One attacker detonated his explosive vest at the first gate of the building, paving the way for the second group of gunmen to enter the facility. The Crisis Response Unit (CRU) forces arrived at the site shortly after the attack and they launched a counter-attack to eliminate the terrorists," the security source said.Hashmat Istankzai, a reporter for Shamshad TV, who managed to escape told that the BBC the attackers were still inside the building (around 1 p.m.) with gunfire being heard."Some of my colleagues were killed and injured. I managed to escape."According to the initial information, one attacker and one security guard were killed and three people were injured. But the number of casualties may change as the gunfire was still continuing, the source told Xinhua. Security personnel were trying to regain control of the building. Shamshad TV quickly went off air after the attack began. More than 100 employees are thought to be inside the building.No group has claimed responsibility for the attack yet.