TBILISI, Georgia -- Georgian counterintelligence agents have arrested 13 people accused of spying for Russia's armed forces.

Shota Ordzhonikidze, deputy chief of counterintelligence in the Interior Ministry, says many of them were military pilots. He says the accused were all recruited by Russian military intelligence.

Of the 13, four are Russian citizens and the rest are citizens of Georgia, a former Soviet republic.

The arrests announced Friday are certain to further strain relations between Georgia and Russia, who fought a brief war in 2008.

Ordzhonikidze says the operation to round up the suspected spies began four years ago.