PESHAWAR, Pakistan — A suicide attacker pretending to offer food to a group of tribal police officers detonated his explosives among them on Thursday, killing at least 22 people as they gathered to break the Ramadan fast on the Afghanistan-Pakistan border, officials and witnesses said.

The attack in Torkham, a post on the main route for moving supplies to NATO and American forces in Afghanistan, took place just before dusk, as the men prepared to eat on the lawn outside their barracks. Because the attacker offered food, he was welcomed to join the gathering in accordance with local tradition during Ramadan, said Sajid Khan, a policeman who witnessed the attack.

A militant group affiliated with the Taliban later claimed responsibility for the attack, and a spokesman for the group called a local reporter to warn of further strikes against security forces if Pakistan did not stop NATO supplies from passing through its territory.

Medical workers described a chaotic scene at the local hospital and the blast site.

“So far, we have 22 bodies brought here, but there are many others, so we don’t know the exact casualty figures,” said Zar Alam Shinwari, a local doctor. “We have asked for ambulances from other towns. The situation is bad.”

It was unclear how many of the dead were police officers.

The group that claimed responsibility, the Dr. Abdullah Azzam Brigade, is based in the Orakzai tribal region and is named after a fiery Palestinian scholar who was a mentor toOsama bin Laden and was killed in a car bomb in Peshawar in 1989.

Earlier on Thursday, at least six people were killed in the South Waziristan tribal region in a missile strike by a remotely controlled United States aircraft aimed at a meeting of local Taliban militants, according to security officials in the area.

The attack took place in the town of Kanigurram, in an area considered to be a stronghold of Waliur Rehman, the man the Taliban chose as its regional leader after Baitullah Mehsud, the head of the Pakistani Taliban, died from injuries suffered in a drone attackearly this month.

A government official, speaking on condition of anonymity, said the number of dead from the strike could rise and that it could include some foreign militants.