ISLAMABAD, Pakistan - Extremists with grenades, guns, and suicide vests stormed two mosques belonging to a minority sect Friday in the eastern city of Lahore, killing at least 76 people.

The coordinated attacks targeting Ahmadis illustrated the vulnerability of groups considered outside the Sunni Muslim mainstream of Pakistani society.

The Ahmadis are one of the country's most beleaguered minority groups. Numbering about two million in Pakistan, they consider themselves Muslims but believe their late-19th-century founder, Mirza Ghulam Ahmad, was a savior foretold by the Quran, Islam's holy book - a heresy for many Muslims, who believe Muhammad was the last prophet.

Ahmadis suffer severe discrimination in Pakistan. They are legally barred from calling themselves Muslims.

The attacks occurred during Friday prayers, when worshipers filled Ahmadi mosques in the Model Town and Garhi Shahu neighborhoods.

The attackers were able to easily get inside, opening up with guns and throwing grenades at terrified worshipers. At the Garhi Shahu mosque, two of the attackers wore suicide vests that they detonated inside the main hall.

At least 91 people were wounded in the attacks.

Geo TV, a Pakistani satellite channel, reported that the Punjabi Taliban, a wing of the Pakistani Taliban comprising several Punjabi extremist groups, claimed responsibility for the attacks.

Punjab is Pakistan's wealthiest and largest province, but it is rife with violent sectarian groups that prey on religious minorities such as Ahmadis, Christians, and Shiite Muslims. In April, Ahmadis were subject to a wave of kidnappings and killings in the central Punjabi city of Faisalabad.

The extremist groups, which include Jaish-e-Mohammed, Lashkar-e-Jhangvi, and Sipah-e-Sahaba, have been officially banned for years, but they operate freely throughout Punjab.

Experts say the provincial government, led by the country's largest opposition party, the Pakistan Muslim League-N, has shied away from cracking down because those extremist groups represent large constituencies that provide political support.

At the Model Town mosque, one worshiper, who would give only his first name, Shahzad, said he and others hid on an upper floor as gunfire rang out in the main hall.

"They were throwing grenades and firing everywhere," Shahzad said. "Our leader told us to stay calm and asked us to pray quietly. I was very afraid and very sure that the terrorists would come upstairs and kill us."

Shahzad said that when he looked down on the main floor, he saw several worshipers lying in pools of blood, many of them with gunshot wounds to their heads. Nearby, an extremist clutching a Kalashnikov assault rifle lay wounded, gasping for breath.

Authorities said two of the Model Town attackers were captured. The third assailant was killed by security forces.

About the same time as the Model Town attack, six extremists stormed into the Ahmadi mosque in the Garhi Shahu neighborhood, which had about 1,000 worshipers. Witnesses said they saw the attackers running inside, armed with assault rifles and lugging duffel bags.

"People outside began running for cover and shouting, 'There are men with guns!' " said Abdul Qayyum, a local resident.

Two of the gunmen used a minaret as a vantage point to fire at police. One of them later descended and detonated his suicide vest, said Khusro Pervez, Lahore's top administrative official.

After a three-hour standoff, police regained control of the mosque and arrested two of the attackers.