Search of Portuguese dam in Madeleine McCann case draws to a ...

Police on Thursday wrapped up the latest search effort in the 16-year-old hunt for missing British girl Madeleine McCann after collecting unspecified samples by a reservoir in Portugal, as a German prosecutor played down hopes of an imminent breakthrough.

Key points:Police and sniffer dogs combed the Portuguese dam site for three daysThe collected material will be handed over to German authoritiesGerman prosecutors have named Christian Brueckner an official suspect in Madeleine McCann's disappearance

Portuguese police said in a statement the three-day operation requested by Germany was now over and that the collected material would be handed over to German authorities after "safeguarding the interests of the investigation still ongoing in Portugal".

Police would not say whether any useful clues were found during the search that involved sniffer dogs, use of a tractor-based tree-cutter and investigators raking the cleared ground in a few small areas.

A source close to the investigation told Reuters there was nothing tangible to report.

German authorities, who have named a suspect in the case, have been helping Portuguese crews comb the remote area inland from the Algarve coastal resort where Madeleine McCann — then aged three — went missing during a family holiday in 2007.

"Of course, there is a certain expectation, but it is not high," prosecutor Christian Wolters told Reuters before the end of the search.

Madeleine McCann disappeared as a three-year-old during a family holiday in Portugal.(AP: file)

It was important to show that authorities were investigating the case, he said.

He added that the investigators were looking for the body, but also for anything that could help the investigation, such as clothing: "A lot is conceivable."

He did not expect the results of the studies of the collected samples to be announced any time soon.

German prosecutors last year named Christian Brueckner an official suspect in Madeleine McCann's disappearance.

Parents Kate and Gerry McCann pose with a missing poster depicting an age-progression computer-generated image of their missing daughter Madeleine in 2012.(AP: Sang Tan, file)

The convicted child abuser and drug dealer is behind bars in Germany for raping a 72-year-old woman in the same part of the Algarve.

Brueckner has denied any involvement in the disappearance. No body has been found.

British police who assisted their Portuguese and German counterparts at the Arade reservoir had left by early on Thursday afternoon, followed by German investigators, who packed up their tents at a camp on a hill.

Reuters