Friends Carol Nolan (20), from Tibradden Close in Walkinstown and Patricia McDonald (21), from Cootehill in Cavan, were found dead on Friday afternoon at their rented Breton house, at Rue de Kerblaisy in the Brittany village of Larmor Plage.

The Commissariat de Police at Lorient yesterday told the Sunday Tribune that he had ruled out any possibility of arson, and was now certain that the smoke spread slowly from a small blaze.

The girls had attended a nightclub on Thursday night and returned home at around 4.30am on Friday morning.

Police have yet to determine exactly how the fire began, but said that it was likely to have started at around 6am. The girls were gradually overcome by smoke inhalation, a police spokesman said yesterday, following post mortems on both bodies which were carried out at the Bodelao Hospital in Lorient. Contrary to some reports yesterday, the girls were not found in their beds, the spokesman confirmed.

Both girls were third-year European Studies students at the Institute of Technology in Tallaght, Dublin, and were on an Erasmus international student exchange programme in the University of Southern Brittany for the current academic year.

The girls' landlord, who lives beside their rented house, discovered the two bodies.

He entered the house around midday on Friday after seeing smoke coming from the house but failed to get a reply at the door. Police were called and an investigation was launched. Police yesterday said the investigation was ongoing, although they were certain the cause of the fire was accidental.

The two students returned to France early last week after spending Christmas with their families. Both girls' families were informed on Friday evening of the tragic incident.

Both the Nolan and McDonald families were yesterday reported to be planning to travel to France either over the weekend or tomorrow. Patricia McDonald was the eldest of three children with a sister, Joanne (19) and a brother, James (16). Her mother Theresa told the media at the weekend that the family was in a state of disbelief. "She was having a great time. She had loads of friends over there. We just can't believe this is happening, " she said.

Carol Nolan has one older brother, David (29). Her mother Celia said that Carol was planning to return home to celebrate her 21st birthday on 29 January. "She was talking about going to a disco in Naas, " her father Brendan said.

Dr Tim Creedon, director of the Institute of Technology, Tallaght yesterday lead tributes to the two girls. He described both as "hard working, successful students who were very popular with their teachers and student colleagues". The college's International Officer is travelling to France to offer assistance as required, Creedon said.

Fine Gael Town Councillor in Cootehill, Aiden Boyle, a friend of the McDonald family, described Patricia as a "lovely, popular and hardworking girl. She was very well known and liked by everyone who knew her. We are really heartbroken by this. It is a huge tragedy for this town."

A Department of Foreign Affairs spokesman said yesterday that staff at the Paris embassy would provide consular assistance to the families of both students to help them with the return of the girls' bodies. In circumstances where there is no suspicion of foul play, French police usually release a body without delay after the post mortem.