The attackers struck as thousands of people were visiting Data Darbar, where a famous Sufi preacher is buried. Extremists consider Sufis to be heretics and have often targeted them in attacks.

The first suicide bomber detonated his explosives in a large underground room where visitors sleep and wash themselves before praying, said Khusro Pervez, the top government official in Lahore.

Minutes later, a second bomber detonated his explosives in a large yard upstairs as people tried to flee the first attack, he said.

Police are still investigating the source of a third blast that followed the two suicide bombers.

At least 25 of those wounded in the attacks are in critical condition, said Pervez.

There was no immediate claim of responsibility for the bombings.

Lahore is Pakistan's second-largest city and capital of its most prosperous province, Punjab. It is a key political, military, and cultural center and has been the scene of some of the most spectacular militant attacks in the country over the past year.

On May 28, gunmen and a suicide squad threw grenades and sprayed bullets in attacks on two mosques in the eastern city packed with Ahmadi worshippers. At least 93 people were killed and dozens wounded.

The government has been criticized for lacking the will to crack down on militants in Punjab, many of whom are part of now-banned groups started with government support in the 1980s and '90s to fight the Soviets in Afghanistan and pressure archenemy India.

Many of these groups have formed links with the Pakistani Taleban, which has recruited militants to carry out attacks in parts of Pakistan far from its sanctuary in the northwest near Afghanistan.

Pakistani authorities believe a dangerous new militant group, out to avenge a deadly army assault on a mosque in Islamabad three years ago, has carried out several major bombings in the capital previously blamed on the Taleban.

The emergence of the Ghazi Force was part of the outrage among many deeply religious Pakistani Muslims over the July 2007 attack by security forces on the Lal Masjid, or Red Mosque, a stronghold of militants.

The fierce attack, in which scores of young, heavily armed religious students died, inspired a new generation of militants. These Pakistanis have turned against a government they felt has betrayed them and, to their dismay, backed the US role in neighboring Afghanistan.

The brief but bloody history of the Ghazi Force illustrates the unintended results of Pakistan's policy of promoting extremists to fight India in the disputed area of Kashmir. That policy, which Pakistan denies it pursues, now threatens regional stability as the US and Pakistan's other Western partners pour billions of dollars into the country to stop the rise of militancy.

The new group is made up of relatives of students who died in the Red Mosque assault. It is named after the students' leader, Maulana Abdul Rashid Ghazi, who was also killed.