Officers from Britain's Operation Grange, a unit set up in 2011 to review Madeleine's case, flew to Portugal's southern Algarve region Sunday night to arrest three burglars, the British newspaper The Mirror reported.
Police confirmed they had sent a Letter of Request to Portuguese police seeking permission to arrest the trio, who were allegedly caught burglarizing a vacation rental neary where the McCanns were staying while on Vacation in Praia da Luz in 2007.
Portuguese police regarded the burglary, which happened shortly before Madeleine was kidnapped, to be unrelated. However, "British officers regard this as an oversight," police said.
A spokesman for Madeleine's parents, Kate and Gerry McCann, said: "The letter is a significant development. It is necessary for British police to request the Portuguese authorities allow them to operate on their turf."
"It means they have the intention of arresting and interviewing X, Y or Z. We don't know who they have their sights on but it's likely it is the burglars," the spokesman said. "Whether the Portuguese will co-operate remains to be seen. It is a very sensitive issue with differences they have had. Police want to be given a chance to arrest key suspects. It doesn't prove they have Madeleine but it will rule them in or out of the investigation and that is important."
No formal arrests have been made in the case.