MOSCOW (AP) — Russia's domestic security agency says two border guards got lost and ended up in Ukraine.

The border guard branch of the Federal Security Service in Crimea said the incident happened early Friday during an exercise in Crimea. The agency added that it expects Ukraine to quickly return the two men back to Russia.

A Ukrainian court has arrested the two men for 15 days pending an official probe.

Russia and Ukraine have been in a tug-of-war following Moscow's annexation of Crimea in 2014 and its support for pro-Russia insurgents in eastern Ukraine. The fighting in eastern Ukraine has left over 10,000 people dead since April 2014.