WASHINGTON (REUTERS) - The father of former U.S. spy agency contractor Edward Snowden said in an interview he is reasonably confident his son will return to the United States as long as certain conditions are met.

Those conditions could include not detaining Snowden before trial, NBC News said on Friday. The NBC report added that he plans to make that point in a letter to U.S. Attorney General Eric Holder to be sent through his lawyer later on Friday.

Snowden's father, in part of the NBC interview that aired on the "Today Show", also said he is concerned his son was being manipulated by others, including people from WikiLeaks.

Snowden fled the United States to Hong Kong in May, a few weeks before publication in the Guardian and the Washington Post of details he provided about secret U.S. government surveillance of Internet and phone traffic.