Deadly bus blast in Philippines

A powerful explosion has ripped through a bus in the southern Philippines, killing at least four people and injuring at least 21 others.

The blast happened at the bus terminal in the town of Digos in the province of Davao del Sur.

Attacks on buses in the region are usually linked to attempts to extort money from bus companies.

But in recent weeks there have been added tensions in the region between the government and separatist rebels.

More than 100 people have been killed in four weeks of fighting, which flared up after the Supreme Court blocked a deal to expand an existing Muslim autonomous zone.

The provincial police chief, Cesario Darantinan, told Reuters news agency that the bus had been waiting for passengers at a terminal in the town of Digos when an explosive device went off inside the vehicle.

"It could have been a crude bomb that was set off remotely," he said.

Some of those in hospital are believed to have seriously injured.