Lahore, Jul 2 (IANS): More than 40 Sufi devotees in this Pakistani city were killed and 175 injured when two suicide bombers struck the famed Data Ganj Baksh shrine packed with worshippers who had congregated for the traditional Thursday prayers.

The terror attack took place late Thursday night when thousands of worshippers had gathered at the white marble mausoleum of 11th century saint Abul Hassan Ali Hajvery, commonly known as Data Ganj Baksh.

The synchronised bombings were carried out by two young men who wore vests stuffed with explosives. The first attacker blew himself up in the basement reserved for ablutions at 10.46 p.m. while the second entered the courtyard just two minutes later and detoned his explosives, police said.

Witnesses said they heard two blasts and then thick smoke filled the air.

"I saw black smoke billowing out from all over the shrine," said a man who was walking past when the explosion occurred. "The area was filled with a burning smell," he added.

"Men, women and children were trying to run in every direction to get away," said a devotee who was in the courtyard when the first blast took place.

"We went into the basement and found hundreds of people screaming and running in all directions. The whole basement area quickly turned into debris."

Mian Sajjad Ahmad, Sajjada Nasheen (in-charge) of the shrine, said that they had been receiving threats and he regretted that lack of security measures led to the incident.

The shrine gives shelter to the homeless and provides free food to the hungry round the clock. Many visitors from other areas also take shelter in the shrine, especially in the basement to sleep.

Wails of the injured tore through the air and people scrambled to get away, said eyewitnesses.

Geo TV quoted an aged worshipper as saying: "My wife and I instantly knew it was some sort of explosion. We walked away from the blast site and were taking stock of the situation when we heard another blast about two minutes later. This one was again about 300 metres away, but it felt a lot closer as we clearly felt the shockwave."

The bomb disposal squad estimated that nearly 20 kg explosives had been used in each suicide jacket.

Senior Superintendent of Police (Operations) Chaudhry Shafiq Ahmad told Dawn that ball-bearings and other material used in the blasts had been collected.

A suspect was taken into custody near the shrine.

Giving details, Lahore Commissioner Khusro Pervaiz Bakhtiar told reporters that the bombers had blown themselves up during a large congregation. Describing the strike as a horrible conspiracy, he said: "Our own people (have) become instruments in the hands of others."

Hundreds of people rushed to the shrine to look for their relatives as news of the attack came in.

Local shopkeepers shut shop immediately after the explosions.

Though the attack took place late night, furious residents of the city came out of their homes to protest the attacks.

They blocked the main road, set tyres on fire and threw stones and bricks at the police. The police fired shots in the air and clashed with the crowds.

This city has witnessed a string of bombings since the Pakistani army took on the Taliban in the restive northwest region last year.

In May this year, over 80 people were killed in gun-and-suicide attacks on two mosques of the minority Ahmadi sect. Before that, in March, over 50 people were killed in twin suicide bombings near a military base in Lahore.

The attack on the Data Ganj Buksh is the first attack on a Sufi shrine in Lahore, the capital of the most populated Punjab province, even though the militants have targeted Sufi mausoleums in the restive northwestern province of Khyber-Pakhtunkhwa in recent years. Many Islamic extremist groups, DPA reports, follow a Takfiri ideology, a puritan interpretation of Islam, which considers those praying to the deceased saints as apostates.

Pakistan President Asif Ali Zardari and Prime Minister Yousuf Raza Gilani condemned the attack and resolved to fight the terrorists. The blasts showed that terrorists have no respect for any religion, Zardari said, adding that such acts would not dent the government's resolve to fight the menace of terrorism and militancy.

The prime minister said: "Such cowardly acts indicate that the terrorists after their defeat in bordering areas have resorted to target innocent citizens in the cities."