U.S. President Joe Biden affirmed on Thursday that they were getting close in on the source of the leak of highly classified US intelligence documents.
This is considered the most serious security breach in a decade.
Last week, the Department of Justice opened a formal criminal investigation after the matter was referred by the Pentagon.
Some of the leaked details are purportedly related to Ukraine's military capabilities and shortcomings, and information about US allies including Israel, South Korea, and Turkey.
Reuters reviewed over 50 of the documents, labeled "Secret" and "Top Secret" but has not independently verified their authenticity. The number of documents leaked is likely to be over 100.
Meanwhile, a number of states questioned the veracity of some of the documents, including Britain, which said there was "a serious level of inaccuracy" in the information.
Biden, who is on a three-day tour of Ireland, pointed out that he was not overly concerned about the leak.
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