Portuguese police announced that they have found no trace of missing four-year-old Madeleine McCann on Friday, after they searched a deserted scrubland area cited in an anonymous letter.

"No evidence was found that anything at all had been buried there," police chief inspector Olegario de Sousa said after the area had been searched with sniffer dogs, not far from where the missing girl vanished from her hotel bedroom on 3 May.

An anonymous letter and map was sent to a Dutch newspaper, De Telegraaf, on Wednesday detailing the supposed location of the body of the missing British four-year-old.

About 10 police cars were parked in the area and officers walked around with dogs in the location that the letter indicated.

Meanwhile, the parents of Madeleine are praying for a breakthrough and still hoping to find their daughter alive.

Kate and Gerry McCann have held onto their Catholic faith throughout their ordeal, regularly attending a local Catholic church as well as recently travelling to Rome to meet Pope Benedict XVI, who prayed for their daughter.

But Mr McCann, a consultant cardiologist, admitted: "If we don't get Madeleine back alive and well, I am sure our faith will be severely tested."

In the interview with The Tablet, a Catholic newspaper, Mr McCann said: "At the end of it, we will still have our faith and we will also have comfort that Madeleine will be looked after. We haven't dwelt on that but I think that is what we will be left with.

"Our friends, our family, the Church have really rallied round. I think that's the key thing for me."

Mrs McCann, a part-time GP, said she had also wondered if her belief was strong enough: "I have felt guilty asking, 'Will this make or break my faith?'

"And yet at the same time you could argue that what's happened in the first place could make or break your faith and it hasn't, it's done the opposite. It has given us hope and strength."