Lõhmus is being held at the Lefortovo pretrial detention facility in Moscow, according to daily Postimees, under suspicion of treasonous activities. He was seized by Russian security agency the FSB on Aug. 13, as reported on ERR News.

"The Estonian Ministry of Foreign Affairs is prepared to provide all-round assistance to an Estonian citizen at his or her request. However, the person in question has not turned to the ministry for assistance," ministry media adviser Liisa Toots told Postimees.

"The Ministry of Foreign Affairs has no more information about the person in question than has been published in the media," Toots added.

The same situation applies to the prime minister's office, who reportedly had no further information on Lõhmus and the charges he faces than have been made public, BNS reports.

The Internal Security Service (ISS) also has issued no comment.

According to Postimees, the nature of the charges Lõhmus faces, i.e. treason, suggest that the Russian authorities consider him one of their own, rather than an Estonian citizen, which would more likely have led to charges of espionage.

Both ISS operative Eston Kohver, seized at the Estonian-Russian border in 2014 and imprisoned for around a year, and businesman Ravio Susi, were held at Lefortovo on espionage charges.

Lõhmus, 38, had been employed at a sawmill in the Russian town of Pskov, approximately 40 kilometers from the border, according to regional daily Pskovskaya Guberniya.

Many residents in Pechory District, which lies along Russia's border with Estonia, hold both Estonian and Russian citizenship.