The Bulgarian unit’s leader was Orlin Roussev, 47, who with his deputy Biser Dzhambazov, 43, and another man, Ivan Stoyanov, pleaded guilty to spying for Russia shortly before the trial, admitting charges of conspiring to collect information intended to be directly or indirectly useful to an enemy.

The Russian government on Monday expelled two British diplomats and gave two weeks for them to exit the country over allegations of espionage. Britain said the allegations are "baseless."