A Moscow court has found Estonian aviation technology businessman Raivo Susi guilty of espionage and sentenced him to 12 years in a high-security prison, Interfax news agency reported.

The court found Susi guilty on the charge of espionage under the Penal Code of the Russian Federation, and handed to him a sentence of 12 years in a high security prison, it stands in the court ruling published on Monday.

The trial was was not open to public, Interfax said.

Susi has categorically denied spying.

Officers of the Russian Federal Security Service (FSB) arrested Susi in Moscow's Sheremetyevo Airport in February 2016 as the Estonian was about to board a flight to Tajikistan.

Susi's lawyer Arkadi Tolpegin has said that all the actions that Susi was accused of took place from 2004-2007.

The investigation was opened at the beginning of 2016.

Information available from online sources shows Susi as owner of several companies in Estonia that engage in the assembly, maintenance, repair and sale of training jet aircraft. His customers were millionaires, and members of the aviation clubs of Russia, Britain, the U.S. and Western Europe.

One of Susi's companies, Aerohooldus OÜ, is currently leasing two L-39 training jet aircraft to the Estonian Defence Forces under a four-year contract effective from 2015.