An explosion killed at least 15 people and injured 20 in Pakistan's eastern city of Lahore Monday, rescue officials said, but it was not immediately clear what caused the blast.

"We have 15 confirmed (fatal) casualties and 20 injured," Jam Sajjad Hussain, a spokesman for the Rescue 1122 service, told AFP.

Bomb blasts by terrorists are common in Pakistan, especially in tribal areas bordering Afghanistan, but attacks in Lahore have become less frequent recently.

Gas cylinder blasts are also common in Pakistan, where gas is used for everything from cooking to powering cars.