Two French genetics research students were tied up, stabbed to death and left in a burning flat in an attack described by a senior British detective yesterday as the most violent he had ever seen.

The bodies of Laurent Bonomo and Gabriel Ferez, both 23, were found in a house in southeast London after neighbours heard an explosion and saw a man running from the scene.

The Metropolitan Police said the biochemistry students working on a DNA project had stab wounds all over their bodies. They were dead before the fire started at Mr Bonomo's rented flat in New Cross late on Sunday, police said. "The extent of their injuries was horrific," said Detective Chief Inspector Mick Duthie. "Everyone working on this case has been deeply shocked by what they've seen. I've never seen injuries like this throughout my career.

"The level of violence used on these two victims was excessive. It's horrendous".

Officers said they did not yet know why the students were attacked, and appealed for anyone who knew them to come forward.

Police are looking at the possibility that they were the victims of mistaken identity.

The pair were on a three-month research project at Imperial College London, one of the world's leading science universities.

They had arrived in London in May and were due to return to France later this month. Media reports said they came from Clermont-Ferrand, central France. Their families travelled from France to identify their bodies on yesterday.

No weapon has been found. Police are searching the area for clues and have seized security camera footage. The London Fire Brigade has launched an investigation into the blaze.