Director of National Intelligence James Clapper pointed in a Senate Intelligence Committee hearing to "the profound damage that his disclosures have caused and continue to cause."

As a consequence, the US is less safe, Clapper said.

The disclosures had caused the loss of intelligence sources and exposed US surveillance efforts to terrorists and other foes, Clapper claimed.

"Snowden claims that he's won and that his mission is accomplished. If that is so, I call on him and his accomplices to facilitate the return of the remaining stolen documents that have not yet been exposed, to prevent even more damage to US security," Clapper said.

Snowden's leaks about the extent of the National Security Agency's surveillance on telephone and internet records prompted an international outcry last year.

US President Barack Obama earlier this month unveiled proposed reforms of US surveillance designed to enhance privacy protections and provide reassurance to US allies.

Revelations that the US spied on communications of allies, including the leaders of Germany and Brazil, were particularly damaging.

German Chancellor Angela Merkel on Wednesday told parliament that the NSA's spying "breaches trust and sows mistrust" and that it had resulted in "less security."

The White House would not comment directly on Merkel's statements, except to point to Obama's reform pledges and says he looked forward to a visit to Washington by Merkel later this year.

Brazilian Foreign Minister Luiz Alberto Figueiredo Machado meanwhile is to meet Thursday with National Security Advisor Susan Rice at the White House.

Brazilian President Dilma Rousseff cancelled a planned state visit to Washington in October over the spying revelations.

NJF/NJF