A powerful bomb exploded near security forces guarding a famous Sufi shrine in Pakistan , killing at least five people and wounding 23 others, police said.

Lahore police chief Ghazanfar Ali said the bombing appeared to target police officers outside the shrine, known as Data Darbar, where Sufi saint Ali Hajveri is buried. Hundreds of pilgrims were inside and outside the shrine when the blast took place, he said.

Sufism refers to a mystical strain of Islam that often involves reverence for local holy figures and shrines. Sunni extremists view Sufism with hostility and have carried out attacks on Sufi celebrations and shrines across the Muslim world.

TV footage showed a badly damaged police vehicle that authorities said was the target.

“It seems police officers who were doing their routine duty outside the Data Darbar shrine were the target,” Ali said, adding that some pilgrims and passers-by were among those wounded. He said the death toll could rise as some of the victims are in critical condition.

Raja Basharat, a senior provincial minister in the Punjab government, said police were still trying to determine the nature of attack, which might have been a suicide bombing. Prime Minister Imran Khan condemned the bombing.

Pakistanis in large numbers visit the shrine, where a pair of suicide attacks in 2010 killed and wounded dozens of people.

Lahore is the capital of eastern Punjab province, which has seen similar attacks in recent years.