PESHAWAR, Pakistan (Reuters) - Pakistani warplanes bombed Taliban positions in the northwest Sunday, killing at least five insurgents, residents said, as militants distributed leaflets warning area tribesmen not to rise up against them.

Fighting has intensified in northwest Pakistan over the past two months, since the military went on the offensive to push back an expanding militant movement that had raised fears for the stability of the nuclear-armed U.S. ally.

The latest air strike happened about 25 km (15 miles) west of Miranshah, the main town in North Waziristan, a Taliban bastion on the Afghan border.

"It was a surprise attack. Fighter jets came, circled around a few times, pounded the militants and flew away. I saw five bodies of militants," Mohammad Khan, a shopkeeper in the area, told Reuters by telephone.

Khan said the casualties could be higher, as two Islamic seminaries used by militants as hideouts were completely destroyed in the bombing.

Earlier, allies of Pakistani Taliban chief Baitullah Mehsud tossed leaflets, or so-called night-letters, into the main market of Miranshah, warning tribesmen not to form committees to fight against them.

"There is a ban on holding any sort of jirga (tribal council)," the leaflet read.

"If any clan or village creates any sort of committee for peace, then its leaders will be killed. There will be no reluctance to launch suicide attacks."

Bolstered by the government's gains against militants, tribal leaders in the northwest have recently begun to form lashkar, or militias, to fight against the Taliban.

The civilian government has won broad support from the public and political parties for its assault against the Taliban, and officials have vowed to crush militancy and defeat Mehsud.

Security forces, near the end of a two-month campaign against the Taliban in the northwestern Swat Valley, have stepped up pressure on Mehsud in his South Waziristan stronghold near the Afghan border and are expected to begin a full offensive there soon.

As fighting intensifies in northwest Pakistan, U.S.-led forces in Afghanistan last Thursday launched a major push against the Taliban in the southern Afghan province of Helmand.

Helmand shares a 200-km (130-mile) desert border with the southwestern Pakistani province of Baluchistan, and the Pakistani army has sent soldiers there to block any Taliban fleeing.

(Reporting by Haji Mujtaba; Writing by Kamran Haider; Editing by Jason Subler and Valerie Lee)