(CNN) -- Police in Portugal are reopening the case of Madeleine McCann, a British girl who was 3 years old when she disappeared while on vacation there with her family in 2007, prosecutors in Portugal said Thursday.
This follows the discovery of new lines of inquiry after an internal review of the original Portuguese investigation, London's Metropolitan Police said.
Madeleine's parents, Kate and Gerry McCann, have been briefed on the decision, the UK police statement said.
Mystery has surrounded Madeleine's disappearance from her family's holiday villa in the Portuguese resort town of Praia da Luz for the past six years.
A unit from the Metropolitan Police has also been working on a new investigation. It issued fresh suspect drawings in the case last week, along with a televised appeal for information, which prompted a flood of calls and e-mails from the public.
Neither her parents nor the detectives investigating her case have given up on one day finding the little girl from Leicestershire, England.
The two police forces' investigations will run in parallel and at the moment are following separate new leads, the Metropolitan Police said Thursday.
The Portuguese and UK police "have a shared determination to do everything possible to discover what happened to Madeleine," said Assistant Commissioner Mark Rowley of the Metropolitan Police.
But, he cautioned, while the latest developments are welcome, the dual investigations are at relatively early stages and much work remains 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," Rowley said.
UK detectives have been trying to reconstruct exactly what happened on the night of May 3, 2007, when Madeleine disappeared from the villa while her parents dined at a nearby restaurant. The girl was just days shy of her fourth birthday.
The discovery last week of a blond girl aged 5 or 6 living with a Roma couple in Greece who proved not to be her biological parents thrust the issue of missing children into the spotlight.
Kate and Gerry McCann told UK media last week that the news from Greece gave them "great hope" that their own daughter, who would now be 10 years old, could be found alive.
About 10 cases of missing children around the world are "being taken very seriously" in connection with the Greek girl's case, including children from the United States, Canada, Poland and France, a spokesman for a Greek children's charity said.
CNN's Lindsay Isaac and Alexander Felton contributed to this report.