Two Russian intelligence officers and two opposition politicians were among 13 people sentenced on Thursday over a 2016 election day plot aimed at toppling Montenegro’s government, killing the prime minister and bringing a pro-Russian alliance to power.

The verdict given in the heavily guarded Montenegro court said that on Oct. 16, 2016, the accused planned to attack state institutions and kill then-Prime Minister Milo Djukanovic, who has led the Adriatic country almost continuously, either as prime minister or president, for three decades.