The policeman leading the hunt for missing youngster Madeleine McCann has said he can't be sure she is still alive.

Little information about the police investigation has been made public, prompting criticism that officers are not doing enough to find the three-year-old.

Today, reports claimed detectives were investigating British paedophiles with links to the Algarve. Portuguese media said authorities in the UK had supplied detectives in the region with information on child abusers who have moved or travel there.

It said specialist detectives from the sex abuse and homicide unit in Lisbon had been dispatched to the holiday region to help with the case.

It was claimed officers saw paedophilia as a possible motive because there had been no ransom demand.

Chief Inspector Oligeario Sousa refused to comment on the claims, but said: "I want to assure the family and all the people involved the professionals are doing the best they can."

On Saturday, Portugal judicial police said they believed Madeleine was still alive but the Chief Inspector admitted: "We have no facts to sustain the child is alive or not. We are searching for the child until the moment she appears. We can say nothing more because we are not magicians."

Hours earlier, Madeleine's mother, Kate, made an appeal to anyone holding her daughter to let her go.

With her husband Gerry - a consultant heart surgeon originally from Glasgow - beside her, she said: "Please, please, do not hurt her. Please do not scare her. We beg you to let Madeleine come home."

The toddler, from Rothley, near Leicester, disappeared on Thursday night while she was left with her brother and sister, two-year-old twins Sean and Amelie, in a holiday flat as her parents dined nearby.