The British parents of missing four-year-old Madeleine McCann, kidnapped in Portugal 11 days ago, told journalists Monday they believe their daughter is alive and safe and pledged to remain in Portugal while the search for her continues.

"Until there is concrete evidence to the contrary, we believe that Madeleine is safe and being looked after," the young girl's father, Gerry McCann, told a brief news conference as his wife, Kate, stood by his side.

The McCanns also expressed their gratitude for an outpouring of "excellent support" from people around the world, including a pot of reward money for Madeleine's safe return that is estimated to have grown to more than £2.6 million (about $5.7 million).

Among the higher-profile contributors were Harry Potter author J.K. Rowling, American Idol judge Simon Cowell and British tycoon and Virgin owner Richard Branson.

Madeleine, whose fourth birthday was Saturday, vanished from her apartment bedroom in the seaside Portuguese resort of Praia da Luz on the evening of May 2 while her parents ate supper about 50 metres away.

Police have said they have no suspects in the case, despite a ground sweep of the area aided by local volunteers. Police also said they had been following up on reports of a white van and a blond foreign woman who appeared to be in her 40s but added that the lead had gone cold.

Still, Kate McCann pledged that she and her husband will not consider leaving Portugal for home until they have more answers.

"We can't even consider returning home at the moment, can't even let it enter my head," she told reporters.

Madeleine was asleep in the apartment with her two-year-old twin siblings on May 2 and the McCanns said they had been checking in on them roughly every 30 minutes. When the parents returned to check on the children again later that evening, they found a window open in the apartment and their daughter missing.

Portuguese detectives are now exploring the possibility that Madeleine was taken out of the local area and may even be out of the country.