The White House, which wants Snowden sent home to face trial for leaking details of government surveillance programs, signaled that President Barack Obama might boycott a summit with President Vladimir Putin in Moscow in September and one official said high-level talks next week were "up in the air".

"We see this as an unfortunate development and we are extremely disappointed by it," White House spokesman Jay Carney said. "We are evaluating the utility of the summit."

Snowden has avoided the hordes of reporters trying to find him since he landed from Hong Kong on June 23, and gave them the slip again as he left the transit area where he had been holed up. Almost unnoticed, he was driven away from the airport by car.