He also attacked Russia for allowing the former NSA computer technician to land in Moscow.

"What's infuriating here is Prime Minister [Vladimir] Putin of Russia aiding and abetting Snowden's escape," Schumer said. "Putin always seems almost eager to put a finger in the eye of the United States.

"That's not how allies should treat one another, and I think it'll have serious consequences for the United States-Russia relationship," he said.

Mike Rogers, chairman of the US House Intelligence Committee said the US government had to exhaust all legal options to get Snowden back to the US.

"When you think about what he says he wants and what his actions are, it defies logic," said Rogers on NBC's , repeating his assertion that Snowden's leaks had damaged US national security.

The US Justice Department said it would seek co-operation from countries where Snowden might travel. Hours later it emgerged that Snowden had applied for asylum in Ecuador.

"The chase is on," California Senator Dianne Feinstein said. "And we'll have to see what happens," she said.

National Security Agency director Keith Alexander said the NSA was overhauling operations to keep closer watch on contractors like the fugitive Snowden, who had top security clearance and "stole some of our secrets".

Alexander, interviewed on ABC television, described Snowden as an NSA computer system administrator with top security clearance who betrayed his nation by taking information from the NSA and fleeing from his base in Hawaii to Hong Kong.

No red flags went up to detect that theft, Alexander said, and the NSA was working to prevent a repeat.

"Clearly, the system did not work as it should have. We are now putting in place actions that would give us the ability to track our system administrators, what they are doing, what they are taking," he said, adding that the NSA was implementing a "two-man rule". He did not elaborate.

Also, "we've changed the passwords. But at the end of the day we have to trust that our people are going to do the right thing".