“The attorney general’s office has decided to reopen the inquiry into the disappearance of Madeleine McCann following a request by police due to new elements,” it said in a statement.
The announcement was greeted with relief by Kate and Gerry McCann, who have never given up their campaign to find their daughter.
“We are very pleased that the investigation to find our missing daughter Madeleine has been officially reopened in Portugal,” the McCanns said in a statement.
“We hope that this will finally lead to her being found and to the discovery of whoever is responsible for this crime.”
Maddie vanished from the holiday apartment where her parents were staying in the southern Algarve resort of Praia da Luz just days before her fourth birthday in May 2007, while they were dining at a nearby tapas bar.
Portuguese authorities closed their investigation into her disappearance in 2008, but Scotland Yard spent two years reviewing it at the British government’s request and opened their own probe in July this year.
Portugal’s Correio da Manha newspaper reported that a police team was sent to review the high-profile case last year with a focus on the possibility of a kidnapping by an organised paedophile network.
“Today’s development is good news,” said Scotland Yard assistant commissioner Mark Rowley.
“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.”
British police would travel regularly to Portugal to coordinate their investigations with local police, Rowley said, warning that there was still “a way to go” in solving the case.
The McCanns have led a six-year campaign to find Madeleine, who they believe was kidnapped and is still alive.
The discovery last week of a young blonde girl in a Roma camp in Greece has resurrected the issue of child kidnapping in Europe, and had “given hope” to Madeleine’s parents, their spokesman said.
British detectives investigating the Maddie case last week published two new electronic images of a man they want to contact in a major new appeal also shown in Germany and the Netherlands.
Police also want to identify two other men, probably with short blond hair and possibly speaking German or Dutch, who had also been seen repeatedly near the apartment.
The British detectives said they had received 2,400 calls and emails since the television appeal, while several hundred calls were also received by the German and Dutch shows.
Detective chief inspector Andy Redwood, who is leading the British investigation, said witnesses had spotted a man carrying a young child fitting Madeleine’s description towards Praia da Luz.
Another man seen carrying a child near to the apartments where the family were staying — who was for years considered the chief suspect — has been excluded from the investigation.
Earlier this month, British police said analysis of mobile phone data from thousands of people who were in Praia da Luz when Madeleine disappeared could provide a new lead.
The detectives have interviewed 442 people over the last couple of years and have identified 41 potential suspects — 15 of them British nationals — although no arrests have been made.
The McCanns are suing a Portuguese detective who wrote a book about the case in which he argues that Madeleine was accidentally killed and implicates the couple.
They are seeking the equivalent of £1 milion (1.2 million euros, $1.6 million) and have tried unsuccessfully to ban the book.