BUCHAREST, Romania (AP) — Moldova said Tuesday it has expelled a Russian diplomat after Moscow opened polling stations for its presidential election in Moldova's pro-Russia breakaway region of Transnistria.

Relations are increasingly fraught between Russia and Moldova, whose pro-Western government has firmly opposed Russia’s full-scale war in neighboring Ukraine.

Moldova summoned Russia’s ambassador, Oleg Vasnetsov, to protest against the Kremlin's decision to open six polling stations in Transnistria “contrary to the position of the Moldovan authorities,” the foreign ministry said.

It said it informed Vasnetsov that an unnamed embassy worker was a “collaborator” who was declared persona non grata and must leave the country.

Russia had previously agreed to open just one polling station at its embassy in Moldova's capital of Chisinau. Russia has opened polling stations in Transnistria in previous presidential elections as well.

Moldovan officials have repeatedly accused Russia of conducting a “hybrid war” against their country by funding anti-government protests, meddling in local elections and running vast disinformation campaigns to try to topple the government and derail the country from its path toward full European Union membership.

Transnistria was declared a breakaway state by pro-Russia forces after a short war in the early 1990s. It isn’t recognized by any U.N. member country, including Russia, which maintains close ties to the region that is home to about 220,000 Russian citizens. Russia maintains about 1,500 troops in Transnistria as so-called peacekeepers, who guard Soviet-era weapons and ammunition stockpiles.

A large number of Russian citizens in Transnistria also hold Moldovan passports.

Moldova is set to hold a referendum on EU membership later this year — along with its own presidential election. Moldova was granted EU candidate member status in June 2022, and Brussels in December of last year said it would open accession negotiations for both Moldova and Ukraine.