In the tiny nation, Moscow paid Orthodox priests, conducted a vote-buying scheme and set up training camps on election interference — all in an effort to derail the Western-leaning government.

It resembled in many ways a summer camp. Barbecues and beach volleyball games were on offer. A wellness spa was called “Relax and Have Fun.”

The men and women who attended the program at a resort complex in a remote part of Serbia also took part in more sinister activities, like learning to break through police cordons and set buildings on fire. They donned flak jackets and trained with assault rifles.

Their counselors, it turned out, were operatives with ties to Russia’s military intelligence service, known as the GRU. Their purpose, according to intelligence officials from three countries who described the activities, was to build a cadre of disciplined shock troops trained in election interference.

The target was tiny Moldova, a country of about three million people that carries outsize importance for President Vladimir V. Putin of Russia.

The Kremlin’s campaign included methods familiar elsewhere in the West, like hacking and disinformation. But in Moldova, its intervention went further than perhaps anywhere else outside Ukraine, and stands as one of the most extensive and audacious plots to date in Mr. Putin’s effort to destabilize the West, the three Western intelligence officials say.

Besides the camp in Serbia, Russian agents ran training programs in Bosnia and Moscow that were designed to turn pro-Russian Moldovans into foot soldiers. Moscow paid hundreds of Orthodox Moldovan priests to recruit voters and to push Russian narratives from the pulpit. And it spent hundreds of millions of dollars on a sophisticated vote-buying scheme financed by a Moldovan billionaire in exile and conceived and operated from Skolkovo, the Kremlin’s knockoff Silicon Valley outside Moscow.

Moscow’s campaign has not stopped. This spring, Russian missiles targeted energy infrastructure that provided service to Moldova, polluting waterways and disrupting electricity flows.

This article is based on interviews with activists who took part in the Russian effort; senior Moldovan law enforcement and security officials; and more than half a dozen European and American intelligence officials. The New York Times also reviewed thousands of documents related to Russia’s attempts to interfere in Moldova’s elections.

Many of those interviewed insisted on speaking anonymously, either to discuss sensitive security operations or because they feared retribution.

Details about Russian efforts in Moldova have emerged in court cases and local reporting, but the scope and extent of the campaign, including the vote-buying scheme and role of Russia’s intelligence services, has not been previously reported.

Publicly, Russian officials have denied interfering in Moldova’s affairs, and have dismissed accusations that Moscow is trying to undermine the West. Last December, Mr. Putin, in an address to military commanders, castigated European leaders for “stoking hysteria” over the threat from Russia.

Soon afterward, though, he gathered the leaders for a secret briefing to deliver the exact opposite message, according to officials from two countries with knowledge of the episode. Their goal for 2026, Mr. Putin told them, is “the collapse of NATO and the E.U. from within,” the people said.