The parents of missing UK girl Madeleine McCann have urged British Prime Minister David Cameron to order a "comprehensive review" of the information surrounding their daughter's disappearance.
Kate and Gerry McCann wrote in a letter to British newspaper The Sun that it was "not right that a young, vulnerable British citizen has essentially been given up on".
"One call might be all that is needed to lead to Madeleine and her abductor," the couple's message said.
"To this end we are seeking a joint independent, transparent and comprehensive review of all information held in relation to Madeleine's disappearance," continued the letter.
A spokesman for the British leader said the government would do "all it can to help them".
A new book written by Kate McCann is being serialised in The Sun, with proceeds going towards boosting dwindling search funds.
The book, Madeleine, is released in the UK on Thursday - the missing toddler's eighth birthday - and is expected to be a best-seller.
In the 384-page account, Kate McCann, 43, admitted she contemplated suicide in the aftermath of the abduction and revealed she was haunted by "a macabre slideshow of vivid pictures".
"The pictures I saw of our Madeleine no sane human being would want in her head, but they were in mine," McCann wrote.
"I had an overwhelming urge to swim out across the ocean, as hard and as fast as I could... until I was so far out and so exhausted I could just allow the water to pull me under and relieve me of this torment," she added.
Madeleine went missing in the Portugese resort of Praia da Luz on May 3, 2007, a few days before her fourth birthday, as her parents and their friends ate at a nearby restaurant.
Five months after Madeleine's disappearance, Portuguese police made Kate and Gerry McCann formal suspects in the case but they were later cleared.
The couple, from Leicestershire in central England, warned that a search fund which they set up to find their daughter was running dry after once standing at £2 million ($4.14 million).