LAHORE: A powerful bomb exploded near security forces guarding a famous Sufi shrine in the eastern city of Lahore on Wednesday, killing at least four people and wounding 20 others, police said.

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

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.

He said the death toll could rise as some of the victims of the bombing are in critical condition.

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 witnessed similar attacks in recent years.