Peshawar, Pakistan ? A suicide bomber killed 67 people Friday at a mosque frequented by tribal elders opposed to the Pakistani Taliban. Hours later, three people died in a grenade attack on another mosque associated with anti-Taliban militia.

The strikes in northwest Pakistan were a reminder of the potency of the Taliban and their al-Qaida allies along the Afghan border despite U.S.-backed army offensives. The Obama administration believes success against insurgents there is key to its hopes of winning the war in Afghanistan.

The Pakistani army has supported the creation of militias to fight the Taliban, who are unpopular in many parts of the northwest. The groups know the region and its inhabitants and are seen as useful in securing cleared areas or stopping militants from moving into their districts.

The insurgents regularly target these groups with suicide attacks and warn residents not to join up with them. On two occasions this year suicide attackers have killed about 100 people attending militia events, while dozens of others have been killed in smaller strikes.

Friday’s first attack happened at midday in the town of Darra Adam Khel, a militant stronghold which lies on the edge of Pakistan’s semiautonomous tribal region.

The bomber, who authorities said appeared to be a teenager, ran into the mosque where several hundred worshippers were gathered for midday prayers on the holiest day of the week. He detonated explosives around his waist.