Shouting "stop religious terrorism," hundreds of Christians marched in Karachi Wednesday after two gunmen invaded the office of a Christian charity, tied up workers and shot seven of them to death, each with a bullet to the head.

The bloodbath in the southern port city shattered hopes that a sweeping crackdown on Islamic militants had quelled the violent groups targeting foreigners and Pakistan's Christian minority.

An eighth person was critically wounded in the attack on the third-floor office of the Institute for Peace and Justice, a Pakistani Christian charity. The victims, all Pakistani Christians, were bound to chairs with their hands behind their backs before being shot, Karachi Police Chief Kamal Shah said.

There was no claim of responsibility and Shah said it was not known who was behind the attack. Police were questioning an office assistant who was tied up and beaten but not shot.

It was the latest in a string of attacks on Christian organizations that have killed at least 36 people and wounded 100 since President Pervez Musharraf's decision to join the war on terrorism in Afghanistan and crack down on extremists at home.

It came a day after gunmen in the western province of Gujarat in neighboring India killed 32 people at a Hindu temple, raising new tensions between the hostile neighbors.

In Karachi, Pakistani authorities were trying to figure out how the gunmen got into the office, which had an electronic door that could only be opened from the inside, he said. The office assistant told police there were two gunmen, Shah said.

The building in a central business district of Karachi was cordoned off, and a female relative of one of the victims was led away sobbing by police. The mother of another victim, 36-year-old Benjamin Talib, collapsed and was taken to the hospital.

The Institute for Peace and Justice has operated in Karachi for 30 years, working with poor municipal and textile laborers to improve working conditions and organize programs with human rights groups.

Pakistan's 3.8 million Christians make up about 2.5 percent of the country's overwhelmingly Muslim population.

Information Minister Nisar Memon denounced the attackers as "enemies of Pakistan."

He said the violence would not shake the nation's resolve. "Pakistan's cooperation with the world community in the war against terrorism will continue," he said.

Many Pakistani Christians complained the government was failing to protect them and some took their outrage out on city officials.

"Shame! Shame! Shame!" a crowd of people shouted at Karachi Mayor Naimatullah Khan when he arrived at the hospital where the bodies were taken.

Later, 400 demonstrators, most of them Christian, marched on the Governor's House, shouting "stop religious terrorism" and demanding protection.

"People in our community now feel more insecure ... our people are being killed," said Bishop Victor Mall, head of the Diocese Church of Pakistan in Multan, an area in Punjab province that has spawned a number of militant Muslim groups.

Shehbaz Bhatti, a Christian who heads the All Pakistan Minorities Alliance, blamed Islamic militants sympathetic to Usama bin Laden's Al Qaeda network and the hard-line Taliban regime ousted from neighboring Afghanistan.

He said Christians felt increasingly insecure in Pakistan. "Our anger is now reaching the boiling point," he said.

Mayor Khan appealed to all Muslims in Pakistan to work with Christians to promote peace.

"Those trying to disturb the peace in Karachi are bent upon exploiting religious sentiments," he said.

In October last year six masked gunmen opened fire on congregants at a Protestant church service in the Punjab city of Behawalpur, killing 15 Christians and a Muslim guard.

On March 17, a grenade attack on a Protestant church in Islamabad's heavily guarded diplomatic quarter killed five people, including an American woman, her 17-year-old daughter and the lone assailant.

On Aug. 9, attackers hurled grenades at worshippers as they were leaving a church on the grounds of a Presbyterian hospital in Taxila, 25 miles west of the capital, Islamabad. Four nurses were killed and 25 people were wounded.

Four days earlier, assailants raided a Christian school 40 miles east of Islamabad, killing six Pakistanis.

But optimism had been growing that authorities were getting the upper hand.

This month, police in Karachi arrested 23 members of Harakat ul-Mujahedeen Al-Almi, a militant group suspected in the June bombing outside the U.S. Consulate as well as the suicide car bomb in May that killed 11 French engineers and abortive plots against a McDonald's and a KFC restaurant.

Police found maps of two churches and a Christian school in Karachi, along with weapons and explosives. That discovery prompted authorities to remove signs from outside some churches set up in private homes and to fortify other Christian sites with sandbag bunkers.