A powerful explosion struck a Shiite mosque in Pakistan's garrison city of Rawalpindi Friday, killing at least three people and wounding several others, police said.

The attack occurred as minority Shiites gathered in the mosque to distribute alms to mark the birthday of the Prophet Mohammed.

"I have seen three dead bodies which are being shifted to hospital. The nature of explosion is immediately unclear but it may be a suicide attack," Muhammad Salim, a local police official, told AFP.

"I can see complete chaos. No more details are available at this moment, but there are dead bodies and injured people inside the mosque," he said.

Eyewitnesses said the explosion was powerful and blew out windows.

"There was a huge bang," one eyewitness, Sadia Widad, told AFP from the area.

"The injured are being taken out of the mosque on carts because ambulances are unable to enter the narrow street."

Nobody has yet claimed responsibility but militants linked to the Taliban and Al-Qaeda have targeted the country's Shiite minority in the past.

A bomb targeting Shiites at a volleyball match killed at least four people and injured eight in Pakistan's restive northwest last Sunday.

The incident happened at the Hussaini ground, owned by the local Shiite community in the Kalaya neighbourhood of the Orakzai tribal district.

Pakistan has strengthened its own offensive against the Taliban since their attack on a military-run school on December 16 killed 150 people, 134 of them children.