Portuguese authorities have reopened their investigation into the disappearance of Madeleine McCann, starting an inquiry that will run alongside a UK police inquiry.
Britain's Metropolitan Police said the Portuguese investigation was being restarted as a result of new lines of inquiry emerging from an internal review.
Portuguese police had shelved their investigation into what happened to the girl in 2008, the year after she vanished.
However, they had supported the British-run inquiry that was launched earlier this year.
Madeleine was three when she disappeared from Praia da Luz in the Algarve in early May 2007.
Her parents, Kate and Gerry McCann, have said they are "very pleased" about the plans to reopen the investigation.
They said they hope it will uncover "the answers we so desperately need".
Detective Chief Inspector Andy Redwood, who is leading the UK team, Assistant Commissioner Mark Rowley and Madeleine's parents met officers in Lisbon last week to be briefed on the Portuguese case.
The new Portuguese lines of inquiry are separate to those being chased by the Met.
Mr Rowley said: "The meeting was very positive, and we and the Policia Judiciara have a shared determination to do everything possible to discover what happened to Madeleine.
"Colleagues in Portugal fully shared with us the developments in their review, and the fact that they were taking the significant step of applying for the investigation to be formally reopened.
"This is a welcome development, but both sides of the investigation are at relatively early stages, with much work remaining to be done.
"This new momentum is encouraging, but we still have a way to go, and as with all major investigations, not all lines of inquiry that look promising will yield results.
"Today's development is good news. Combined with the formal reopening of the Portuguese investigation today, and our ever closer working relationship, I believe that we have the best opportunity yet to finally understand what happened to Madeleine."