LAC-MEGANTIC, Canada (AFP) - Police said on Tuesday they were looking at criminal negligence as the cause of worst train disaster in recent Canadian history, while the US firm involved denied any responsibility.

The death toll rose from 13 to 15 with the discovery of two more bodies after the explosion and inferno produced by the derailment of a train carrying oil near Montreal. Around 40 people are still missing.

Quebec police are looking for "evidence that might allow the filing of criminal charges," said police inspector Michel Forget. He did not specify against whom.

Standing 200m from the scene of the disaster, he said the hypothesis of criminal negligence was "under consideration."

Meanwhile the head of the US rail company at the centre of the disaster blamed firefighters for the derailment, as investigators combed through smouldering debris for evidence.

"We are very hopeful we will find more bodies," said Forget.

Residents of the small Quebec town of Lac-Megantic, part of which was flattened by the blast and subsequent inferno, began returning to their homes.

The explosion unleashed a wall of fire that tore through homes and businesses in Lac-Megantic, located east of Montreal near the US border.