ISLAMABAD, Pakistan — The serenity of prayers at a mosque during the Muslim holy month of Ramadan was transformed into a bloodbath Friday in Pakistan's remote tribal area, when a bomb ripped through the congregation and killed at least 40 people and injured more than 100 others, officials said.

The suspected suicide blast came during Friday afternoon prayers in a village near Jamrud, the main town in the Khyber part of the tribal zone, close to the Afghanistan border. It was almost certainly the work of al Qaida-linked extremists. Some news reports put the death toll at more than 50.

While no group immediately claimed responsibility, residents speculated that the bombing was a revenge attack by Pakistani Taliban for recent clashes with local tribesmen. The mosque, of the main Sunni sect, was not a particularly well-known place of worship and the surrounding area isn't considered dangerous; most of Khyber isn't controlled by the Taliban or other militant groups, unlike many other parts of the tribal area.

The injured were rushed to hospitals in Peshawar, about 30 minutes away by road, mainly in private cars as there were few ambulances available. Between 300 and 400 people were at the mosque, which would have been packed during Ramadan, normally a time of piety and quiet contemplation.

"I don't know what happened or where the bomber came from," said a dazed Mustafa Kamal, who was injured in the blast and appeared on local television lying in his hospital bed. "Is this any way for Muslims to behave? Whoever did this cannot be a Muslim, no matter what they say."

At the mosque, after the casualties were taken away, television pictures showed blood splattered across the floor and on prayer caps and mats. The walls and roof were scarred by shrapnel — tell-tale signs of a suicide vest, which is usually packed with ball-bearings, nails and other metal projectiles designed to shred those close by.

Zahid, a local resident who did not want to give his full name out of fear of retribution, told McClatchy that the bomber was not in the middle of the mosque but to one side, against a wall.

"If he had stood in the middle of the congregation, the carnage would have been to all sides and he'd have killed maybe a hundred," said Zahid.

The bomb exploded in an area inhabited by the Kuki khel tribe. Earlier this month, a Kuki khel militia blew up vehicles carrying a group of Pakistani Taliban in the Tirah valley, a remote and dangerous part of Khyber. They had attacked the men of Tariq Afridi, one of the most feared commanders of the main Pakistani Taliban group.

Also in recent days, locals said they had repelled a Taliban incursion into the area.

"The message here from the Taliban is that we can attack you at your home," Zahid said.

Most of the supplies transiting through Pakistan for the U.S.-led NATO force in Afghanistan must go through Khyber, the most developed part of the tribal area. But the main Pakistani Taliban group, Tehreek-e-Taliban Pakistan, fights in its own country and is closely tied to al Qaida, rarely taking part in the war in Afghanistan.

A local official, Iqbal Khan, said that the bomb went off just as worshipers were leaving after prayers.

Extremist groups usually don't claim responsibility for bombings at mosques and other public places so as not to damage their image, leaving a vacuum in which conspiracies flourish about who's behind them.

"If this was a suicide attack, then they should do it in Afghanistan, against American or British soldiers. We are Muslims, so why target us? said Saeed ur Rehman, who lives close to the blast site.

Separately, a missile fired from a U.S. drone aircraft elsewhere in the tribal area reportedly killed four suspected militants Friday in South Waziristan.

(Shah is a McClatchy special correspondent.)

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