The Chicago Tribune journalist, who was on assignment for National Geographic magazine when he was arrested, had been held for more than a month on espionage charges.

His Chadian driver and interpreter were also freed.

In a brief news conference in the Sudanese capital Salopek said that his "treatment was excellent" while in detention.

He had been accused of passing information illegally, writing "false news" and entering the country without a visa.

National Geographic contested the accusations throughout and said that Salopek "had no agenda other than to fairly and accurately report on the region".

Bill Richardson, the governor of the US state of New Mexico, travelled to Sudan on Friday to meet with Omar al-Bashir, the president of Sudan, and persuaded him to release Salopek and his colleagues.

Richardson said during the news conference: "It was a humanitarian gesture.

"All the problems can always be solved through negotiations."

Salopek said: "I am grateful to the Sudanese president al Bashir, governor Richardson, the US ambassador, and of course the US consul who visited me in detention, and was helpful for me and my colleagues."

In 2001, Salopek won a Pulitzer prize for international reporting for his work covering Africa. In 1998, he won a Pulitzer for explanatory reporting for his coverage of the Human Genome Diversity Project. At the time of his arrest he was working on an article about the people, culture and history of the sub-Saharan region known as the Sahel.