ROGACA, Serbia (AP) — When Elena Koposova signed an open letter against Russia's full-scale invasion of Ukraine, she didn’t expect a backlash in her newly adopted home state of Serbia.

After all, Serbia is formally seeking to join the European Union while adopting all the democratic values that go along with the membership, she thought. Now, she sees she was wrong.

TENSIONS RISE AMID CLAIMS OF RUSSIA, SERBIA INTERFERENCE IN KOSOVO FOLLOWING RECENT BLOODSHED

Two years after signing the letter, the 54-year-old Russian woman is appealing an expulsion order after she was declared a threat to the national security of Serbia and her residency permit was revoked. The beleaguered literature translator said the only reason she could think of is the anti-war petition that she had signed.

"I am not an activist, but I did sign an anti-war letter when the Russian aggression in Ukraine just started," she said in an interview. "Even not being an activist, I couldn’t just be quiet about it. So, I just put my name on the open letter where it was said that the war is a crime, and we must all unite to stop it."

Koposova is not alone. Serbia opened its borders in recent years to tens of thousands of Russians fleeing the government of President Vladimir Putin and the war in Ukraine. Russian pro-democracy activists in the Balkan country now say at least a dozen recently faced entry bans or had their residency permits revoked on grounds that they pose a threat to Serbia’s security.

At least eight others are afraid to speak publicly about their legal problems with the Serbian authorities, fearing it could only jeopardize their chance of remaining in the country together with their families, Russian anti-war campaigners say.

"It was very sudden, very shocking," Koposova said of the moment she received the expulsion order, which did not explain the reason for the measure, only declaring that she poses "a threat to national security" and that she must leave the country within 30 days.

She and her husband have built a modern house on a piece of land in a remote village outside Belgrade where they live with two children, ages 6 and 14, who are attending local school and preschool classes.

Rights activists say the residency problems point to a close relation between Serbia's increasingly autocratic president, Aleksandar Vučić, and Putin, despite Serbia’s formal EU bid. Vučić has refused to join Western sanctions against the traditional Slavic ally while allowing Moscow propaganda outlets such as RT and Sputnik to spread their narrative throughout the Balkans.

"The authorities in Belgrade and the authorities in Moscow are politically very close," said Predrag Petrović, research coordinator at the Belgrade Centre for Security Policy, an independent think tank that has sought an explanation from the Interior Ministry about the measures against the Russians.

"People who are critical of Putin’s regime present a big threat to the regime in Moscow," Petrović said. "This is why these people are being targeted by the Serbian authorities."

Serbian officials so far haven't commented about the reported cases involving Russian citizens, and Serbia’s Interior Ministry hasn't responded to an email from The Associated Press requesting an interview or a comment on the issue.

Since the war in Ukraine started two years ago, many Russians came to Serbia because they don't need visas to enter the friendly Balkan state, a potential stepping stone for possible future emigration to the West. Many were dodging the draft, while others, like the Koposova family, who came earlier, simply were fed up with Putin’s government and sought a better life somewhere outside of Russia.

Peter Nikitin, one of the founders of the pro-democracy Russian Democratic Society, himself spent two days at Belgrade airport last summer when his entry permit was revoked, although he has a Serbian wife and has lived in Serbia for seven years. Nikitin was later allowed into the country, but a legal procedure regarding his residency papers is ongoing.

"I have no doubt that this is being done on direct orders from Russia, either via the embassy or directly from Moscow," insisted Nikitin, whose group has also organized protests against the war in Ukraine and demonstrations demanding freedom for political prisoners including Alexei Navalny, a Russian opposition leader and a Putin critic who died on Feb. 16 in an Arctic penal colony in Russia.

Nikitin said other anti-war activists who faced scrutiny by Serbian authorities include fellow founder of the RDS group, Vladimir Volokhonsky, who now lives in Germany.

Also under sanctions were Yevgeny Irzhansky, who organized concerts by anti-Putin bands in Serbia and who has since moved to Argentina with his wife, and Ilya Zernov, a young Russian who was banned from returning to Serbia after being attacked by a far-right Serbian nationalist when he tried to erase a wall painting calling for death to Ukraine in downtown Belgrade.

Nikitin said that the goal of these measures is to intimidate anti-war campaigners.

"The only explanation for that is that they want to scare everyone," he said. "Because if you can’t sign an anti-war letter, then there’s really nothing you can do. And it does have a chilling effect."

"The point is the anti-war Russians are not protesting here against anyone in Serbia," Nikitin said. "We are only concerned with our own country and with our neighboring country, which is suffering from our country right now."

Serbia’s close relations with Russia date back centuries and the two countries also share a common Slavic origin and Orthodox Christian religion. Russia has supported Serbia’s bid to retain its claim on Kosovo, a former province that declared independence in 2008 with Western backing.

Serbia and Russia also maintain close links between their security services.

Former Serbian state security chief Aleksandar Vulin, who was sanctioned by the U.S. for aiding Russia’s "malign" influence in the Balkan region, recently received a decoration from the Federal Security Service of Russia for close cooperation between the two spy agencies. Vulin reportedly was involved in wiretapping prominent Russian opposition activists who met in Belgrade on the eve of the war in Ukraine and who were later jailed in Russia.

For Koposova, the decision by Serbian authorities to kick her out of the country, means that she and her family could lose everything if her appeal is rejected.

The family can’t go back to Russia because they have sold all their property, are now labelled as anti-Putin and her husband could be drafted into the army to fight in Ukraine, Koposova said.

"This house is our only house, the only house that our kids have," she said, with tears in her eyes.