Four suspects in the disappearance of Madeleine McCann are to be questioned in Portugal.
Scotland Yard officers will sit in on the questioning, starting on Tuesday (local time), but would not be able to ask questions, BBC reported.
Eight key witnesses would also be questioned.
All of the suspects were Portuguese nationals, although some were Russian born, and would attend questioning voluntarily after being identified as suspects by British police, BBC reported.
The interviews were expected to take two or more days.
The three-year-old vanished while holidaying with her parents in Praia da Luz in 2007.
British police announced it was launching an investigation into Madeleine's disappearance last July - after spending two years reviewing the case under the codename Operation Grange.
Its teams investigating the disappearance went to Portugal earlier this month to survey and dig at an area of bush near the resort where she was last seen, but they found nothing of interest to the case.
Madeleine, whose parents Gerry and Kate live in Leicestershire, England, was days away from her fourth birthday when she was abducted.