Madeleine McCann disappeared on 3 May 2007 from her bed in a holiday apartment in Praia da Luz in the Algarve region of Portugal.
Metropolitan Police Assistant Commissioner Mark Rowley said they still hoped they could provide answers to the disappearance:
I know we have a significant line of inquiry which is worth pursuing, and because it's worth pursuing it could provide an answer, but until we've gone through it I won't know whether we are going to get there or not.
A number of newspapers have run front pages on the news line.
Four detectives are currently working on the case in the United Kingdom, a scaled back operation from the 30 in 2011.
More than £11m has been spent on the investigation so far.
Kate and Gerry McCann wrote in a Facebook message that they were "bracing ourselves for the next couple of weeks":
Ten years - there's no easy way to say it, describe it, accept it.
I remember when Madeleine first disappeared I couldn't even begin to consider anything in terms of years...
And now here we are... Madeleine, our Madeleine - ten years.
Mail on Sunday journalist Dan Hodges has recommended that people concern themselves with other cases of missing children, rather than increasing interest in this one case, that has eclipsed all others for nearly a decade.
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