LONDON (Reuters) - Two experts from Britain's child sex abuse agency have joined Portuguese police in the search for missing toddler Madeleine McCann amid mounting criticism of the investigation.
The psychologist and a behavioural analyst work for a government-backed body linked to the Serious and Organised Crime Agency.
"They went out at the request of Portuguese police and are working with them," said a spokeswoman for the London-based Child Exploitation and Online Protection Centre.
"This is to ensure that they have the full range of expertise available for every possible avenue of the investigation."
They are expected to advise their Portuguese counterparts on the behavioural traits of paedophiles.
Three-year-old Madeleine vanished from an apartment in a holiday village in southern Portugal last Thursday while her parents were at a nearby restaurant.
Portuguese police have launched a huge operation to find her. They have searched 500 apartments, followed up hundreds of leads and interviewed scores of people.
But critics say they were slow to respond, failed to alert border police until the morning after Madeleine disappeared and have given out little information to help find her.
The Daily Mirror branded the police "Clueless" in a front page headline.
Senior officers and diplomats have defended the investigation. They say they are doing all they can, but are prevented by Portuguese law from releasing sensitive operational details.
"You have a system where the secrecy of justice prevails," Portugal's Ambassador to London Antonio Santana Carlos told BBC radio. "That is a constitutional principle that you cannot change.
"That is why the investigators cannot disclose the ways and methods that they are pursuing."
Portuguese police would welcome any help "in this difficult case", he added.
The British ambassador to Portugal John Buck said he met Madeleine's parents Gerry and Kate McCann for an hour on Tuesday and that they expressed gratitude for the Portuguese authorities' efforts.