Michala Bendixen, Denmark’s country coordinator at Refugees Welcome, a nonprofit, said the policy threatened to tear Syrian families apart. “The only purpose is to make Denmark the last place to choose as an asylum seeker,” she said in an interview.

Because the Danish government does not maintain diplomatic relationships with Mr. al-Assad’s government, the authorities cannot forcibly deport refugees. Since most of them are unwilling to return voluntarily, those who lost their appeals after their residency was revoked are likely to be sent to departure centers.

The Danish authorities did not respond to questions about why the policy was implemented for Syrians and how many had been sent to departure centers.

collapsed economy and half of its prewar population displaced. Mr. al-Assad has reclaimed control of two-thirds of its territory, including the Damascus area. He has also called on Syrians to come back, but many say they won’t for one reason: Mr. al-Assad himself.

Syrian Network for Human Rights, and the European Union’s asylum body has warned that voluntary returnees are at risk of detention, torture and death.

“The absence of fighting in some areas does not mean that people can go back safely,” said Ms. Slente of the Danish Refugee Council.

Ms. al-Asseh, the chemistry and biotechnology student, said she had tried to focus on her studies since learning that her residency permit would be revoked. Yet she said the thought of starting over again terrified her.

“I’m not a danger. I’m not a criminal,” she said. “I just want to live here.”

Rick Gladstone contributed reporting.

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