HELSINKI (AP) — Estonian officials say a former military officer and his father have been arrested on suspicion of treason and spying for Russia.

The state prosecutor's office and the Estonian Internal Security Service said in a joint statement Wednesday that Deniss Metsavas, born in 1980, and Pjotr Volin, born in 1953, were arrested Sept. 3.

The men are suspected of passing Estonian state secrets and other classified information to Russia's military intelligence service GRU for a period of more than five years.

Metsavas had served with Estonia's armed forces for years in various positions including a mission with NATO troops in Afghanistan. He advanced to the rank of major in 2015.

Estonia, a NATO member and a former Soviet republic, has witnessed several high-profile spy cases since its independence in 1991.