BUENOS AIRES (Reuters) - Fugitive former U.S. spy contractor Edward Snowden controls dangerous information that could become the United States' "worst nightmare" if revealed, a journalist familiar with the data said in a newspaper interview.

Glenn Greenwald, the Guardian journalist who first published the documents Snowden leaked, said in a newspaper interview published on Saturday that the U.S. government should be careful in its pursuit of the former computer analyst.

"Snowden has enough information to cause harm to the U.S. government in a single minute than any other person has ever had," Greenwald said in an interview in Rio de Janeiro with the Argentinean daily La Nacion.

"The U.S. government should be on its knees every day begging that nothing happen to Snowden, because if something does happen to him, all the information will be revealed and it could be its worst nightmare."

Snowden, who is sought by Washington on espionage charges after revealing details of secret surveillance programs, has been stranded at a Moscow airport since June 23 and is now seeking refuge in Russia until he can secure safe passage to Latin America, where several counties have offered him asylum.

Greenwald told Reuters on Tuesday that Snowden would likely accept asylum in Venezuela, one of three Latin American countries that have made that offer.

Snowden's leaks on U.S. spying secrets, including eavesdropping on global email traffic, have upset Washington's friends and foes alike.

Latin American leaders lashed out at the United States after Greenwald reported in a Brazilian newspaper that the U.S. targeted most of the region with spying programs that monitored Internet traffic.

Washington has urged nations not to give Snowden safe passage.

Greenwald said in his interview with La Nacion that documents Snowden has tucked away in different parts of the world detail which U.S. spy programs capture transmissions in Latin America and how they work.

"One way of intercepting communications is through a telephone company in the United States that has contracts with telecommunications companies in most Latin American countries," Greenwald said, without specifying which company.

(Writing by Mitra Taj; Editing by Sandra Maler)