British police said Thursday they were opening their own investigation into the 2007 disappearance of toddler Madeleine McCann in Portugal and had identified 38 "persons of interest" across Europe.

A two-year review of the original Portuguese investigation, which is officially closed, had resulted in some "genuinely new lines of inquiry", said Detective Chief Inspector Andy Redwood of Scotland Yard police headquarters.

"We have identified 38 persons of interest from a number of European countries. Twelve of those people are UK nationals who we believe were in Portugal at the time Madeleine disappeared," he said.

These people are not necessarily all potential suspects, and none of them are thought to be known to Gerry and Kate McCann, who have never given up the search for their daughter.

Police said they believed that Madeleine, who was only three when she vanished from the family's holiday flat in Praia da Luz on Portugal's south coast in May 2007, may still be alive.

Since 2011, Redwood's team has gathered more than 30,000 documents, visited Portugal 16 times, carried out new witness interviews and generated new theories.

"We continue to believe that there is a possibility that Madeleine is alive," he said.

The McCanns, who were at dinner nearby when their daughter disappeared, launched a global publicity campaign to find her and her picture was circulated around the world.

Their spokesman welcomed the new police investigation.

"They see it as a huge step forward in establishing what happened and hope that it will lead to bringing to justice whoever was responsible for Madeleine's abduction," he said.