A suicide bomber has attacked the funeral of an anti-Taliban tribal elder in northwest Pakistan, killing at least 20 people.

Thursday's blast took place in the Lower Dir tribal area, as more than 100 people gathered during funeral prayers.

Police say the bomber targeted members of an anti-Taliban militia.

More than 50 people were wounded.

No one has claimed responsibility for the attack, but the Pakistani Taliban has stepped up attacks on pro-government tribes.

On Tuesday, gunmen opened fire on a school bus, killing four children and the driver. The Taliban claimed responsibility for the shooting, saying the children were from a local tribe that has been fighting insurgents in the region.