The separate attacks came in a region where the Pakistani military has clashed for months with Islamic insurgents allied with Taliban and al Qaeda militants who are involved in attacks on American and NATO troops in neighboring Afghanistan.
U.S. officials have praised Pakistan for getting tougher on militants, but the offensives have escalated extremist bloodshed in the Muslim nation where anti-American sentiment runs deep.
The first suicide attacker killed 17 people and wounded 40 at a gathering of tribesmen in a militia formed to combat insurgents, government and hospital officials said. A purported spokesman for a Taliban-linked group claimed responsibility for the attack.
Late Thursday, another suicide bomber rammed his vehicle into a checkpoint manned by security forces near a police compound in the Swat Valley, killing at least two paramilitary troopers and wounding at least 20 other people, officials said.
Pakistan launched an offensive in Bajur three months ago to dismantle what it said was a virtual Taliban mini-state from where militants were flowing into Afghanistan.
Salarzai tribesmen were preparing to stage an assault on local militant hide-outs when the suicide bomber struck, said Iqbal Khattak, a government official. Malik Rahimullah, a tribal elder, said the bomb exploded as soon as the armed tribesmen began to move.
Witnesses said they saw a young man rush into the crowd before the explosion.
Amir Khan, a tribesman, said that the scene was littered with severed limbs and that several tribal elders who were instrumental in starting the militia were among the dead.
Khattak said 11 bodies were taken to the main hospital in Khar, the area's main city. Mohammad Kareem, a hospital official, said later that at least six of some 45 wounded people had died and that more than a dozen of the remaining injured were in serious condition.
Later, a man who said he was a spokesman for a Taliban-linked group, Caravan-e-Naimatullah, claimed it was behind the bombing. Little is known about the group, but earlier this year it briefly took over a handful of schools in the region.
The man, who identified himself as Abdul Rehman, called an Associated Press reporter and other local journalists with the claim. The main Pakistani Taliban spokesman, Maulvi Umar, could not immediately be reached for comment.
The army claims to have killed some 1,500 insurgents in the Bajur offensive. At least 73 soldiers and 95 civilians have also died, it says. Lack of security and government restrictions mean accounts of the fighting cannot be verified.
Government troops also have carried out operations in the Swat Valley, a former tourist area now wracked by violence where the suicide bomber blasted the road checkpoint Thursday night.
Officials in the Mingora area reported a huge explosion and said there was extensive damage followed by a firefight that made it difficult for authorities to search the area for casualties.
Senior police official Dilawar Bangash said two paramilitary officers were killed, and Abdullah Khan, an official at a nearby hospital, said at least 20 wounded had been brought in.
Militants have responded to the military offensives - as well as stepped-up U.S. missile strikes in parts of Pakistan's border zone - with a wave of suicide attacks that are adding to concern about the U.S.-allied country's stability.
The militants also have gone after the tribal militias, including beheading some of the elders involved. A suicide attack in October in the nearby Orakzai tribal region against another such militia killed dozens.
Also Thursday, airstrikes on militant hide-outs elsewhere in Bajur killed 19 suspected insurgents, the military said.