The ability of contractor-turned-fugitive Edward Snowden to evade arrest is raising new concerns among U.S. officials about the security of top-secret documents he is believed to have in his possession — and about the possibility that he could willingly share them with those who assist his escape.

It’s unclear whether officials in Hong Kong or in Russia, where Snowden fled over the weekend, obtained any of the classified material. A spokesman for the anti-secrecy group WikiLeaks, which has been assisting the former National Security Agency contractor, strenuously denied reports that foreign governments had made copies of the documents.

“This rumor that is being spread is a fabrication and just plays into the propaganda by the administration here that somehow Mr. Snowden is cooperating with Russian or Chinese authorities,” spokesman Kristinn Hrafnsson said in a phone interview Monday.

Nonetheless, in 2010 and 2011, WikiLeaks published hundreds of thousands of sensitive U.S. documents it obtained from Army Pfc. Bradley Manning, and co-founder Julian Assange suggested in a teleconference call with reporters Monday that the group was interested in gaining access to the documents Snowden had obtained.

“In relation to publishing such material, of course WikiLeaks is in the business of publishing documents that are supposed to be suppressed,” Assange said. He declined to say whether Snowden had shared any of the material.

The NSA has teams of analysts scouring systems that they think Snowden may have accessed, officials said. Analysts are seeking to retrace his steps online and to assemble a catalogue of the material he may have taken.

“They think he copied so much stuff — that almost everything that place does, he has,” said one former government official, referring to the NSA, where Snowden worked as a contractor for Booz Allen Hamilton while in the NSA’s Hawaii facility. “Everyone’s nervous about what the next thing will be, what will be exposed.”

Glenn Greenwald, the Guardian columnist who has published a series of stories based on documents provided by Snowden, said he has exercised discretion in choosing what to disclose. Snowden, too, has said he was selective in choosing what to disclose.

“I know that he has in his possession thousands of documents, which, if published, would impose crippling damage on the United States’ surveillance capabilities and systems around the world,” Greenwald told CNN. “He has never done any of that.”

The Guardian, Greenwald said on “Meet the Press” on Sunday, has withheld “the majority of things that he gave us pursuant not only to his instruction, but to our duty as journalists.”

Over the past several weeks, The Washington Post and the Guardian have published articles and portions of documents that describe two major surveillance programs. One, called PRISM, deals with the interception of e-mail and other Internet content of foreign terrorism suspects thought to be located overseas. The other involves the amassing of a database of Americans’ phone call records — numbers dialed and received, length of call, but no content — which can be searched for a specific phone number when there is “reasonable, articulable” suspicion of a terrorist plot or activity associated with the number.