The blast, a day after the beginning of the Muslim holy month of Ramadan, went off at a police checkpoint near the Data Darbar, one of the largest Muslim shrines in South Asia, wrote reuters.com. 

"Police was the prime target in this attack. We are collecting forensic evidences to ascertain the nature of the blast," said Ashfaq Khan, deputy inspector general of police operations in Lahore, adding that nine people were killed and 24 wounded.

Muhammad Farooq, a spokesman for the city’s rescue services, said at least seven of the wounded were in critical condition.

Police set up checkpoints on main roads leading to the shrine and hospitals were placed on alert, officials said.

The attack was claimed by the Hizbul Ahrar, a splinter group of the Pakistani Taliban, who said they were targeting the police.

"This attack was carried out at a time when there were no civilians near the police," a spokesman for the militant group, Abdul Aziz Yousafzai, said in a statement.

The Pakistani Taliban have been fighting the government for years.

Sufis, who follow a mystical form of Islam that has been practiced in South Asia for centuries, have been regularly attacked by hardline Sunni Muslim militants in the past.

In 2010, two suicide bombers struck the Data Darbar shrine killing 42 people and wounding 175, in an attack officials said was carried out by the Pakistani Taliban.

Militant violence has since declined sharply in Pakistan following a sustained crackdown in recent years. Over the past two years Lahore, Pakistan’s second largest city, has been free of the kind of attacks that were once common.

However, officials warned that the attack showed the need for vigilance during Ramadan.

"People should remain aware of their surroundings when going to pray," said a Punjab provincial minister, Mian Aslam.

Police said a general security alert was in force but there had been no specific warning about a threat to the Data Darbar, which attracts large numbers of visitors.