Belgian police are questioning a man named as the main suspect in the case of two girls who disappeared from a street party in Liège, the town where the serial paedophile murderer Marc Dutroux abducted two of his victims 11 years ago.

Abdullah Ait Oud gave himself up late last night after seeing his name on a television news report on the two girls, step-sisters Nathalie Mahy, 10, and Stacy Lemmens, 7.

But although he was questioned until 5am this morning and is due to be questioned again today, there was no sign of a breakthrough.

The faces of the two girls, who disappeared in the early hours of Saturday, have been staring from the front pages of every newspaper and 30,000 posters across the country. The authorities, desperate not to repeat their incompetence in tracking down Dutroux, have put 60 officers on the case.

Yesterday, they suspended their search after five days of combing the neighbourhood, including helicopter searches of the River Meuse, yielded nothing.

There have been no sightings, and the girls’ computers and mobile phones have yielded no clues.

Anne Bourgauigmont, the investigative prosecutor, said that police had searched everywhere the girls might have been but had found nothing.

Nathalie and Stacy, whose family has a history of domestic problems, were last seen at 1.30am on Saturday playing beside a bouncy castle outside the Les Armuriers café in the neighbourhood of Saint-Leonard.

Catherine Dizier, Nathalie’s mother, and Thierry Lemmens, Stacy’s father, who are in a relationship, were drinking heavily inside the café, surrounded by their four other children.

The parents, who have been criticised for keeping young children in a bar so late, and recently surrendered their one-year-old baby to social services, discovered that the older girls were missing when they prepared to go home.

"Everyone in the café searched for the young girls, but without success," Julio Blazquez, the bar owner and cousin of Mr Lemmens, said. Across the neighbourhood, windows are now covered with posters of the girls.

Mr Ait Oud, initially named as a "primary witness," is the boyfriend of one of the waitresses in the bar. He is reported to have spent the evening there and to have left at around 1.30am.

Murielle and Jean-François, who run a corner shop, said that they were in shock. "Everyone asks the question — where are they? The more time passes the more the anxiety mounts," they said.

Mme Dizier said: "It is true that it is an ordeal, but one must keep things together for the children. I have no news. (Nathalie) will know, and Stacy also, that they are being looked for. It is necessary that they keep up their courage."

Belgium was shaken by the failure of the authorities to capture Dutroux, who abducted, raped and murdered four girls and abducted, serially raped and held hostage two others.

In June 1995 Julie Lejeune and Melissa Russo, both 8, vanished as they played outside their house in Liège. Their bodies were found a year later in shallow graves in Dutroux’s garden. He was jailed for life.

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