A homemade bomb was the likely cause of the blast that hit the vehicle shortly after it left a bus depot in the town of Midsayap on Mindanao island, local police chief Superintendent Chino Mamburam said.

'The IED (improvised explosive device) exploded inside the van. Initial reports said at least three were killed and (many others) were wounded,' Mr Mamburam said.

Mr Mamburam described the explosion as 'powerful' and cited witness accounts saying that many of the victims were bloodied and sprawled on the ground.

No motive for the attack has yet been established and no group has claimed responsibility. Islamic militants including those from the Moro Islamic Liberation Front (MILF) are known to operate in the area.

The MILF has been waging a decades-old for an independent Islamic state on Mindanao.

Peace talks have been suspended since December, and the group has recently warned of fresh hostilities following a decision by the Malaysian government to pull out peacekeepers. -- AFP