PODGORICA, Montenegro — A key witness in the trial of 14 suspected plotters to topple Montenegro’s government on Thursday directly implicated an alleged Russian secret service operative in organizing the coup attempt by supplying money and defining goals in order to prevent the small Balkan nation from joining NATO.

Aleksandar Sindjelic testified in court that the Russian, Eduard Shishmakov, gave him money to organize about 500 people to trigger disturbances in the capital, Podgorica, on the day of last year’s parliamentary election.

Sindjelic said that Shishmakov ‘‘asked no questions about how much money would be spent’’ as long as the then Montenegrin prime minister, Milo Djukanovic, is removed from power, ‘‘dead or alive.’’

Russia has denied involvement in the alleged plot. Montenegro joined NATO in June as the Western military alliance’s 29th member, despite strong opposition from Moscow, which considers the small Adriatic country a historic Slavic ally and is opposed to NATO’s enlargement.

The 14 defendants, mostly Serbs, are charged with ‘‘creating a criminal organization’’ with the aim of undermining Montenegro’s constitutional order and thwarting the pro-Western government’s bid to join NATO. The trial opened in September.

ASSOCIATED PRESS