Two French exchange students found dead after a fire in south-east London were the victims of a ''frenzied, horrible and horrific attack'' having been bound and stabbed repeatedly in the head, neck and torso before the house was set alight.

Laurent Bonomo, of Velaux, and Gabriel Ferez, of Prouzel, both 23, were found lying in the living area of the ground-floor bedsit. Bonomo had been stabbed 196 times with up to 100 injuries inflicted after he was already dead, police said. Ferez had 47 wounds.

Detective Chief Inspector Mick Duthie, of the Metropolitan police, today described their injuries as the worst he had seen in his policing career. "These were two young French students who were visitors to our country and had been in London for only a matter of weeks. They were talented students working on a dream project.

"The level of violence used on these two victims was excessive - it was horrendous. The extent of the injuries are horrific. Everyone working on this case, including myself, has been deeply shocked by what we have seen. I have never seen injuries like this throughout my career.''

The pair arrived in London in May to study bioengineering and DNA at Imperial College under an exchange programme with the Polytech Clermont-Ferrand in central France. Their three-month placement had been due to finish at the end of this month.

Detectives said they believed a burglary at the rented flat six days earlier, in which a laptop was stolen, could be linked to the case.

Police were called to the fire in Sterling Gardens, a residential cul de sac in New Cross, at about 10pm on Sunday.

The fire started with an explosion, police said; the property was severely damaged and there was a smell of flammable liquid. It was extinguished quickly but the men were dead before it took hold.

A white male was seen running from the block shortly after the explosion. No weapon has been recovered, and forensic examinations at the scene are said to be ''extremely complex''. Duthie said: "I do not know why these boys were killed or who killed them. I do believe, however, that whoever is responsible must have been bloodstained when they left.

"I would not say this was a professional attack. I would say it was a frenzied, horrible, horrific attack. "I imagine it would take some considerable amount of time to inflict the nature of the injuries."

Bonomo had spoken to his girlfriend in the early hours of Sunday morning. He and Ferez were thought to have been playing computer games together when attacked. Police said there was no evidence of forced entry and keys may have been used, allowing an attacker to surprise them.

A neighbour, Christina Ramires, 32, from Brazil, said she arrived home five minutes after the bang. She said a Spanish friend, also a neighbour, told her she saw two men banging on the window of the flat prior to a "very strong sound" that she took for an explosion.

Ramires said that when she arrived she could see through the open door of the flat, which was blackened and greasy. It had also been broken into three or four months ago, before the students moved in, she said. Another neighbour, who did not want to be named, was told by police after the burglary six days ago that one of the students had been in the shower and disturbed the intruder, who ran off.

Duthie said it may have been a case of mistaken identity. "We cannot find anything in these two young men's background to suggest they were involved in any criminality, that they had done anything wrong. They were here as students."

A college spokesman said Bonomo had been studying a parasite that can spread from cats to human foetuses. Ferez's research was on using bacteria to create ethanol for use as fuel.

Nicky Crowhurst, 25, a student who shared a laboratory with Ferez in the biochemistry building, said he was a "really nice guy ... it's a huge shock. I can't believe it. Him and his mate were always in the lab. They had only been here a little while. He was a quiet guy but really friendly."

Professor Steve Matthews, who worked closely with Bonomo, said he was an intelligent young man with a bright future. "They were both very likeable chaps. Laurent was particularly mature and well-rounded. He was a keen tennis fan and looking forward to following the French players at Wimbledon. "We are all stunned and shocked, to say the least. Our thoughts are with their families and Laurent's girlfriend."

Sir Roy Anderson, the Imperial College rector, said the thoughts of the community were with the men's families. "Laurent and Gabriel had bright futures ahead of them and it is dreadful that their lives should end so soon," he said.

Members of the victims' families travelled from France to identify their sons' bodies this morning. Duthie appealed for anyone who knew the men at Imperial College or saw anything strange in New Cross on Sunday night to come forward. "I need to build up a picture of these two young men. What were they doing in the hours leading up to the murder?''

"I also appeal to those people who worked with and knew Laurent and Gabriel at Imperial College. What were they like? Where did they go? Who did they meet? Where did they socialise? This attacker was horrific. I ask everybody - please rack your brains.''