Six gunmen opened gunfire on a Christian church service in Pakistan Sunday morning, killing at least 16 worshippers and seriously injuring five others, according to officials.

The rampage took place at 9 a.m. at St. Dominic's Church in the town of Behawalpur. There was no immediate confirmation that the attack was related to recent unrest in Pakistan over U.S.-led airstrikes on Afghanistan, but a Palestinian band of terrorists was believed to have been involved. 

Survivors said worshippers tried to flee and hide under pews to escape what they called an indiscriminate hail of bullets. Witnesses said the unidentified masked men were armed with automatic weapons and bags full of ammunition and sprayed bullets into the congregation where 45 to 50 people were worshipping. 

Among the dead were a 3-year-old child and a police officer providing security.

"Some of them lay down. Some begged for mercy. They didn't listen," said Ali Shah, a man in his early 20s who was in the front pew of St. Dominic's when the men burst in.

Condemning the attacks, Pakistani President General Pervez Musharraf expressed deep shock and sorrow over the killing of innocent people.

Residents said the church is Roman Catholic, but that Protestants also were participating in services Sunday morning, as usual, because they do not have their own church in the area.

Authorities in Pakistan's four provinces ordered increased security at Christian churches Sunday afternoon.

Eight bodies were taken to the Civil Hospital of Behawalpur, and eight more remained outside the church Sunday afternoon, said Dr. Altaf Malik, medical superintendent of the Civil Hospital of Behawalpur. He said "at least five" more people were being treated for bullet wounds.

Another emergency room physician, Dr. Umar Farooq, said four of the dead were children under 12, four were women and eight were men.

A priest at the church who identified himself only as Father Joseph said the priest conducting the morning services, Father Emanuel, was one of those slain. Police could not immediately confirm that.

Behawalpur Police Chief Haris Ikram, reached by telephone from Islamabad, also put the number of dead at 16. He said all were Christian except one — a Muslim police officer named Mohammad Salim. He had no further information on why a Muslim was among the dead, though Father Joseph said the officer was guarding the gate of the church when he was shot.

There was no immediate claim of responsibility for the attack, but intelligence officials said members of a banned Islamic group were under suspicion. They gave no details.

Police said no arrests were immediately made. A city police dispatcher in Behawalpur, reached by telephone, said the situation was under control.

There have been religious tensions between Sunni and Shiite Muslims in the area, but this was the first such attack on Christians in recent memory, authorities said.

Police said at least 100 people were in the church when six unidentified attackers arrived on motorcycles and sprayed it with gunfire.

Shamoon Masih, 34, who was shot in the leg and the arm, said most of those who died belonged to two families. He said the gunmen didn't select particular victims but merely fired into clumps of people.

"They had no mercy for the children. They had no mercy for the women. They could see that small children were being hit by bullets, but they kept firing," Masih said.

The gunmen fled after firing weapons for about two minutes, Masih said. He said he carried several children outside the church before passing out from his wounds.

Malik said that after the shootings, grieving family members angered that their loved ones could not saved came to the hospital, screaming at doctors and destroying some medical equipment. They were not charged with anything.

"We remained calm. We behaved in a sensible manner, because we knew they were grieving," the doctor said.

In 1997, in the southern city of Rahim Yar Khan, hundreds of Muslims burned 13 churches after clashing with Christians they accused of desecrating the Quran, the Muslim holy book. Christians said the Muslims invented the pretext to occupy their land.

Shehbaz Bhatti, president of Pakistan's Christian Liberation Front, condemned the incident as "barbaric" and demanded the government make quick arrests. He also exhorted the government to provide security to Christians living in Pakistan.

Pakistan, whose full name is the Islamic Republic of Pakistan, is 97 percent Muslim. The remaining 3 percent includes the country's few Christians.

The Associated Press contributed to this report.