A former US national security agency (NSA) employee on Monday pleaded guilty to six counts of attempting to transmit classified information to a Russian agent, the US justice department said in a statement.

Jareh Sebastian Dalke, 31, was employed as an NSA cyber specialist last year.

He admitted that between August and September 2022, in order to demonstrate both his "legitimate access and willingness to share," he used an encrypted email account to transmit excerpts of three classified documents to an individual he believed to be a Russian agent.

"In actuality, that person was an FBI online covert employee," the US justice department said, adding that the three documents in question were classified as top secret.

Mr Dalke requested USD 85,000 in return for all the information he had, claiming it "would be of value to Russia", the statement reads.

The FBI arrested Mr Dalke on 28 September, moments after he transmitted the files.

As part of his plea agreement, the NSA former employee admitted that he willfully transmitted files "with the intent and reason to believe the information would be used to injure the United States and to benefit Russia".

He now faces a maximum penalty of up to life in prison, with the sentencing scheduled for April 2024.