KOHAT - An army helicopter killed five Taliban militants on Friday in restive Hangu, taking the death toll in three days of fighting to 13, government and military officials said. Authorities launched the offensive in the increasingly troubled district of Hangu on Wednesday after Taliban insurgents occupying the area killed 17 paramilitary troops in an ambush and threatened to kill some 49 troops and officials being held hostage. Early Friday morning the army helicopter spotted a vehicle filled with fighters in an area close to the Orakzai tribal region, previously one of the most peaceful of seven semi-autonomous tribal lands. "The helicopter fired at a vehicle in Zargari area, killing five militants and wounding six," a government official in the region said. After the attack, militants managed to take away their wounded comrades, while the dead were shifted to Hangu, according to officials. A military official in the region confirmed the action. He said 13 militants had been killed in the past few days. Residents and military officials said the security forces followed up by targeting militant positions in the surrounding hills with artillery and helicopter gunships. "Ten militants have been killed and five army troops injured since the launch of the operation," said chief military spokesman Major General Athar Abbas. The spokesman said the army had cleared the town of Zargari in Hangu and was now sweeping through surrounding areas. Many militants had fled to the adjoining tribal district of Orakzai, which borders Afghanistan. "The operation will continue until the time the entire area is cleared of militants," the spokesman said. Hundreds of villagers fled the combat zone on Friday, after officials relaxed a curfew on a main road leading to Kohat, a garrison town about 40 km northeast of Hangu. Meanwhile, six persons were killed and 13 wounded in a clash between two groups in Tirah valley in Khyber Agency, reports a private TV channel on Friday. Clashes between Lashkar-e-Islam and Ansarul Islam continued for three weeks in Tirah valley. In Friday's clash, six persons were killed and 13 wounded. More than 140 people have so far been killed and over 400 wounded in the clashes between the LI and the AI during two years.