MIRANSHAH (Agencies) Forces backed by helicopter gunships attacked a militant hideout in North Waziristan on Friday, killing two militants, officials said. The attack in North Waziristan coincided with a visit by US Defence Secretary Robert Gates aimed at persuading Pakistan to expand its military campaign against Afghan militants in lawless ethnic Pashtun lands who cross the border to fight US troops. An intense exchange of fire is going on between militants and the security forces, said an intelligence official in the region who declined to be identified. The attack took place on the outskirts of Miranshah in an old refugee camp now home to both Afghan migrants and Pakistanis. Authorities also slapped an indefinite curfew and conducted searches in the area, the official said. Two militants had been killed as two gunship helicopters attacked a suspected militant camp, another security official said. Six suspected militants have been arrested in the house-to-house search. They are local tribesmen, the security official said, but asked not to be named as he was not authorised to speak to the media. He said one person - a civilian - was killed and two wounded when troops opened fire on them for violating the curfew. A regional government official confirmed the death and the attack, and said that local mosques had announced the curfew beginning around dawn on Friday. Troops besieged the camp early in the morning and two attack helicopters shelled the suspected hideouts, destroying one house, he added. Residents said shops, markets and schools were shut in the area on Friday. North Waziristan is a bastion of the Taliban, Al-Qaeda-linked militants and the Haqqani network, known for attacking US and NATO troops in Afghanistan, and the US has been targeting the area with drone missile strikes. Pakistan sent about 30,000 troops backed by fighter jets and helicopter gunships into battle against the Taliban in neighbouring South Waziristan in October, and says they are making progress and militants are fleeing. During a visit to Pakistan that ended Friday, Gates said he would ask Islamabad about plans to broaden its campaign to North Waziristan. Military spokesman Major General Athar Abbas responded by saying it would take between six months to a year to completely stabilise South Waziristan, which was needed before security forces opened up any new fronts.