Estonia's top prosecutors say authorities have detained a Russian citizen suspected of working as an agent of the Russia's top domestic security agency. They say the man was suspected of preparing a computer-related crime, among others.

Prosecutor Inna Ombler said Tuesday the detention last week means "bigger damage was prevented." She said Estonian state institutions were targeted but didn't disclose details.

Ombler said the man was working for the Russian Federal Security Service — the main KGB successor agency — against Estonia and had committed "a serious crime." He was not identified.

In 2015 and 2016, three men were convicted and jailed for cooperation with Russian special services in Estonia, a former Soviet republic.