A very slim majority (50.17%) voted yes in Sunday's referendum to inserting a clause in the constitution that would define EU membership as a goal, with fewer than 1.5% of the ballots still to be counted.

President Maia Sandu, who is also seeking re-election, wants Moldova, a small country nestled between EU member Romania and Ukraine, to join the bloc by 2030.

"This vote took place under unprecedented interference and intimidation by Russia and its proxies, aiming to destabilize the democratic processes in the Republic of Moldova," Peter Stano, the EU spokesperson, said.

Russia denies the allegations of meddling. On Monday, the Kremlin branded Moldova's votes as "unfree."

The referendum, along with the presidential election—whose first round also took place on Sunday—is seen as a test of whether the former Soviet republic can finally break free from Moscow's sphere of influence.

Before the vote, Moldovan authorities said Ilan Shor, a fugitive tycoon who lives in Russia, had made concerted attempts to meddle in the referendum and election. The authorities said they had taken down online resources that hosted disinformation and had uncovered a program in Russia to train Moldovans to participate in mass unrest.

"This is an ongoing effort from Russia and its proxies—not only in Moldova; indeed, also against our countries—and it's a long-term fight. They don't have boundaries. We, as the European Union... respect certain principles, including the laws, but Russia and its actors and its proxies do not respect that," Stano said.