ISLAMABAD, June 26 (Xinhua) -- At least three security men were killed and 18 others injured in a roadside bomb blast in Pakistan's tribal area bordering Afghanistan on Friday.

    A bomb hit a convoy of security forces heading to Bannu, a main city in North West Frontier Province from Miranshah, the center of North Waziristan tribal agency, at 8 a.m. local time (0200 GMT), the News Network International (NNI) news agency reported.

    Three soldiers died at the scene while 18 others were injured who were flown to a military hospital in Bannu in helicopters. Two injured are in critical condition, doctors said.

    Officials said that a vehicle was completely destroyed and three were slightly damaged in the attack.

    The security forces shelled suspected hideouts of the militants in Miranshah and Mir Ali areas shortly after the blast. One person was killed and two others injured in firing from the security forces, locals said.

    The security forces closed roads between Bannu and Miranshah for few hours after the blast.

    Pakistani Taliban leaders in Waziristan, Mullah Nazir and HafizGul Bahadar said that peace agreements with the government stood ineffective after the United States drone attacks. A Taliban commander Shamsullah threatened Thursday that they would step up attacks if U.S. did not stop drone attacks in Waziristan, according to the NNI.