At least 20 people were killed and 77 others injured in two bomb blasts at a Roman Catholic cathedral on the southern Philippine island of Jolo, where the Abu Sayyaf group and other armed fighters are active.

The first bomb went off in or near the cathedral of Jolo, the capital of Sulu province, followed by a second blast outside the compound as government forces were responding to the attack, security officials said.

Al Jazeera's Victoria Gatenby reports.