Pakistani troops are deployed after an attack on Shiite Muslim worshippers during a religious procession, Tuesday in Quetta, Pakistan.(AP/Arshad Butt)

CREDIT: (AP/Arshad Butt)

QUETTA, Pakistan (AP) - Armed men opened fire on Shiite Muslim worshippers during a religious procession in a city in southwestern Pakistan on Tuesday, killing at least 41 people and wounding more than 150 others, authorities told The Associated Press. The city mayor declared an immediate curfew.

Officials reported an explosion and gunfire in a congested area of Quetta, the main city in southwest Baluchistan province, as a procession of hundreds of Shiite Muslims marking Ashoura, the most important day in the Muslim holy month of Muharram, passed by.

Soon after, a Sunni Muslim mosque, a television network office and several shops were set afire as Shiites rioted in parts of the city, and an exchange of gunfire took place near the scene of the initial attack, police said.

Mohammed Wasim, a doctor at the Central Government Hospital in Quetta, said the facility had received 19 bodies. The Combined Military Hospital reported 22 bodies were brought in since the attack early Tuesday afternoon.

Qamar Zaman, an assistant police inspector in Quetta, said that more than 150 people had been injured, some of them critically.

Government officials said the carnage was an effort by extremist groups to destabilize the country. President Gen. Pervez Musharraf has become a staunch ally of the U.S. war on terrorism, earning the ire of Islamic fundamentalists. He narrowly escaped two assassination attempts in December.

"Obviously, the purpose of this attack was to create unrest," Information Minister Sheikh Rashid Ahmed told AP. "This is a very sad incident and we condemn it."

The violence occurred hours after a series of co-ordinated blasts in Iraq struck major Shiite Muslim shrines in Karbala and Baghdad, killing scores of religious pilgrims. There was no indication the attacks were connected.

Mayor Abdul Rahim Kakar told AP that he had imposed an immediate curfew in the city of 1.2 million to maintain law and order. He said troops and paramilitary forces had been deployed and were bringing the situation under control.

"I was present near the procession when we first heard an explosion and then some people fired shots," he said. "We still do not know what kind of explosion it was."

No arrests have been made.

Meanwhile, two people - one Shiite and one Sunni - were killed and 40 other people wounded in a clash between Shiite and Sunni Muslims in Phalia, a town in Punjab province, about 160 kilometres east of Islamabad, said Nisar Ali Shah, a local police official.

The shootout happened during a Shiite procession, and people from the two sides then set several houses on fire, Shah said.

In Quetta, gunshots continued to ring out in the city nearly an hour after the killings, said Khyzar Hayyat, another police official. "The situation is very bad," he said.

Riaz Khan, Quetta's police chief, said that a Sunni mosque was set afire and was partially destroyed. Also, there was an exchange of fire between Shiite Muslims and unidentified rivals, he said.

Ijaz Khan, a reporter for the private GEO television network, said six unidentified people entered the GEO office there and set it afire. The office was empty and no one was injured. Last week, the network had run a talk show that allegedly aired offensive comments against Shiites.

Quetta was the site of one of the deadliest acts of sectarian violence in years in Pakistan. Attackers armed with machine-guns and grenades stormed a Shiite Muslim mosque in the city in July, killing 50 people praying inside.

Police said a leading suspect in the July attack is the brother-in-law of al-Qaida terrorist Ramzi Yousef, convicted in the 1993 bombing of the World Trade Center in New York.

Shiites are a substantial minority in Quetta. Sectarian violence runs strong in Quetta's Baluchistan province, where radical Islamic groups share power with more moderate Sunni parties.

However, tensions largely centre on the religious divisions that also exist in Iraq.

Allama Hassan Turabi, a senior Pakistani Shiite leader, demanded that President Gen. Pervez Musharraf - who has repeatedly vowed to defeat extremism in the Islamic country - sack government officials including the interior minister for failing to prevent Tuesday's attack.

"This is not the first attack against us. Our people are not safe at homes. They are not safe in mosques," he told AP by telephone from Karachi.

Security had been stepped up nationwide in anticipation of Muharram, a month of mourning when Shiite Muslims recall the seventh-century death of Hussein, grandson of Islam's prophet, Muhammad.

Shiites mark the occasion with religious processions, wearing black clothes as a sign of mourning and whipping themselves, in a sign of penitence over Hussein's death.

Most of Pakistan's Sunni and Shiite Muslims live peacefully together, but small radical groups on both sides are responsible for frequent attacks. About 97 per cent of Pakistan's population is Muslim, and Sunnis outnumber Shiites by a ratio of about four to one.