Montenegro's prosecutors say two Russian citizens are among those suspected of involvement in an alleged election day plot to assassinate the country's prime minister and take power because of his government's NATO membership bid.

A spokeswoman for the Special Prosecution on Monday confirmed media reports that 21 people are being investigated, including the two Russian and three Serbian citizens. She spoke to the AP on condition of anonymity because of the ongoing investigation.

Some 20 people were arrested in Montenegro during the Oct. 16 general election, but some have since been released. Two Russian operatives reportedly have been deported from neighboring Serbia after they monitored Montenegrin Prime Minister Milo Djukanovic's movements.

Russia strongly opposes the NATO bid by its traditional ally Montenegro, but denies involvement in the alleged coup attempt.