Lisbon - Portuguese police hunting for a British four-year-old missing since May believe she may be dead and are looking for her body, a source close to the inquiry said on Wednesday.

"The latest developments in the investigation indicate that police are looking for a body," the unnamed source told Lusa news agency, adding however that police have not ruled out the possibility of finding the girl alive.

Portuguese police have neither officially confirmed nor denied the report.

Madeleine McCann will by this weekend have been missing for 100 days after she disappeared from a hotel room in the southern Portuguese resort of Praia da Luz where she and her two-year-old twin siblings were sleeping while her parents were dining at a nearby restaurant.

According to media reports, the investigation has recently taken a new turn after police, using dogs and ultraviolet light, found traces of blood from a dead person on one of the walls of the room where little "Maddie" was last seen.

A British laboratory is currently analysing the blood samples, a source in the investigation told the Portuguese news agency.

"We have put together a working team of both Portuguese and British police officers. All decisions are being made in common," the investigator said.

Portugal's main daily Diario de Noticias reported on Wednesday that the joint police team has used telephone wiretaps and intercepted emails from the girl's parents and their circle of friends which has led them to raise the possibility that Maddie may be dead.

The police "have never accused the McCann couple of anything", an official told Lusa. "But in a case like this, until we are certain, everyone is suspect."

Portuguese television on Wednesday showed Gerry and Kate McCann visiting the police station at Portimao in south Portugal. The nature of the visit was not known.

However, the McCanns, who have waged a high-profile media campaign to find their daughter, including pledges of reward money from celebrities like Harry Potter author JK Rowling, have met weekly with police to learn the latest on the investigation.

Police also this week resumed searches along Portugal's Algarve coast, using information from experts on ocean currents in the region.

A spokesperson for the McCanns, Justine McGuinness, published on Wednesday a list of events to be held Saturday to mark the 100 days since Madeleine's disappearance, including church masses in both Portugal and Britain as well as releasing posters and balloons.

In another twist in the case on Wednesday, Belgian authorities said that DNA taken from a bottle at a Belgian cafe, following a reported sighting of the missing girl, was that of a man.

The girl in question was accompanied by a man speaking with a Dutch accent and a woman speaking English, in a town near the Dutch border.

Police had taken the bottle and drinking straw for DNA testing believing that the blonde girl seen at the cafe table had drunk from it.

Officials said that the DNA test results "don't mean that the presence of Maddie can be excluded," and that the investigation was continuing.