Security has been stepped up outside Christian monuments in Pakistan

Crying and denouncing violence, a huge crowd of Christians and Muslims crowded into the church compound where the killings took place, with many blaming pro-Taleban hardliners for the attack.

The Pakistani Government has announced a thorough investigation and security has been stepped up at Christian churches across the country.

More than 100 activists from militant Islamic groups were detained in overnight raids in southern districts of Punjab after the church attack, Reuters news agency reported.

At the service, Reverend Andrew Frances, the Catholic bishop of Punjab, told people to remain peaceful, and follow the Christian principle of turning the other cheek.

But many of the angry mourners chanted slogans calling for revenge and demanding protection.

There was heavy police security as 13 of the bodies were taken in a procession of vehicles to a nearby Christian graveyard for burial.

Long-term strategy

President Pervez Musharraf has condemned the killings as "an act of terrorism."

"My government and the law enforcement agencies will do everything possible so that whoever committed this gruesome act is caught and given exemplary punishment," he said.

President Musharraf also promised a long-term strategy to counter terrorism and sectarian extremism.

Unidentified masked gunmen on motorcycles opened fire indiscriminately on the congregation as they prayed on Sunday morning.

Witnesses said the attackers shouted "Allahu Akbar" and "Graveyard of Christians - Pakistan and Afghanistan", before opening fire.

Survivors said the gunmen locked the doors and sprayed fire at the Protestant congregation who were using the Roman Catholic church of Saint Dominic's at the time.

Pleas for mercy were ignored, witnesses said.

No one has so far said they carried out the attack, but the local community has blamed pro-Taleban groups who have held recent demonstrations in the town to denounce the US-led strikes on Afghanistan.

Christians tense

The area has a history of tensions between Sunni and Shi'a Muslim extremists, and hundreds of Muslims have died in sectarian violence over the years.

But Sunday's shooting, police said, is the first such attack on Christians in the region, which is near the border with India.

Some Christian neighbourhoods had, however, already stepped their security.

The BBC's Susannah Price in Islamabad says extremists groups may be trying to portray the current Afghan crisis as a war between Christians and Muslims.

Christians make up about 1% of Pakistan's 120 million population.

In 1997, Muslim rioters in southern Punjab burned and looted hundreds of Christians' homes and ransacked 13 churches and a school, accusing some Christians of committing blasphemy against the Prophet Mohammed.