UK police helped "develop" evidence against Madeleine McCann's parents, according to the latest US diplomatic cables published by Wikileaks.
The American ambassador to Portugal, Al Hoffman, said the claim was made by his British counterpart, Alexander Wykeham Ellis, at a meeting in September 2007.
The cable did not specify what evidence was alleged to have been gathered.
The McCanns said Portuguese authorities had subsequently said there was no evidence against them.
Details of the cable, which was sent to Washington by the US ambassador, have been published in the Guardian newspaper.
Mr Hoffman wrote: "Madeleine McCann's disappearance in the south of Portugal in May 2007 has generated international media attention with controversy surrounding the Portuguese-led police investigation and the actions of Madeleine's parents.
"Without delving into the details of the case, Ellis admitted that the British police had developed the current evidence against the McCann parents, and he stressed that authorities from both countries were working co-operatively.
"He commented that the media frenzy was to be expected and was acceptable as long as government officials keep their comments behind closed doors."
Madeleine McCann was aged three when she disappeared from a holiday apartment in the Algarve resort of Praia da Luz in May 2007.
Her parents Kate and Gerry McCann had official status as suspects, or arguido, until the Portuguese authorities shelved their investigation in July 2008.
A spokesman for the McCanns said: "This is an entirely historic note that is more than three years old.
"Subsequently, Kate and Gerry had their arguido status lifted, with the Portuguese authorities making it perfectly clear that there was absolutely no evidence to implicate them in Madeleine's disappearance whatsoever.
"To this day, they continue to work tirelessly on the search for their daughter, co-operating when appropriate with both the Portuguese and British authorities."
The details are contained in the latest in a series confidential US diplomatic cables released by Wikileaks to appear in the Guardian and several other newspapers around the world.