BELGRADE, Serbia – Serbian police said Friday they arrested two Serbs sought by Montenegro for alleged involvement in a pro-Russian plot to overthrow the Balkan country’s government.

Police said that Nemanja Ristic and Predrag Bogicevic were arrested on an international warrant issued by Montenegro. Ristic was later released from custody pending the extradition proceedings, but he isn’t allowed to leave the country, Belgrade’s Higher Court said.

It wasn’t immediately clear when the two could be extradited.

Montenegro also has issued international warrants for the arrest of two Russians for alleged “terrorist” activities, including plans to kill the prime minister and take over parliament on election day in October.

The two Russians, reportedly members of a Russian military spy agency, allegedly co-ordinated the whole operation from Serbia and tracked the movements of Montenegro’s then-Prime Minister Milo Djukanovic. They have reportedly been allowed to return to Russia.

The Kremlin has denied involvement, but has actively supported local groups that oppose having Montenegro, a traditional Slavic ally, become the 29th member of NATO. Montenegro is expected to wrap up the process later this year.

Ristic, one of the Serb suspects, appeared in a group photo with Russian Foreign Minister Sergey Lavrov during his visit to Belgrade last month.

Montenegro has arrested around 20 people in the alleged coup plot.