Simon Ostrovsky, a journalist for Brooklyn-based Vice News, has been held captive since Tuesday, a spokeswoman for pro-Russia insurgents in Slovyansk, Ukraine, has confirmed. Vyacheslav Ponomarev, the self-described mayor of Slovyansk, said there are no plans to release the American journalist.

"We need prisoners," Ponomarev was quoted in as saying. "They take ours, drive them to Kiev, torture them. Well, we've done the same."

Stella Khoraeva, a spokeswoman for pro-Russian insurgents, claimed Ostrovsky was initially captured for spying on behalf of Ukrainian ultra-nationalists. Later, Khoraeva told The Daily Beast that the insurgents had planned to take Ostrovsky. “We knew where he was going and the men manning the checkpoint were told to look out for him,” she said.

Jen Psaki, the U.S. State Department spokeswoman, said U.S. authorities are “deeply concerned” about the situation and are working to resolve it.

“We condemn any such actions, and all recent hostage-takings in eastern Ukraine, which directly violate commitments made in the Geneva joint statement,” she said, referring to the preliminary agreement to solve the crisis, signed last week in Switzerland. “We call on Russia to use its influence with these groups to secure the immediate and safe release of all hostages in eastern Ukraine.”

Ostrovsky is among more than a dozen people who have been detained during the ongoing crisis in eastern Ukraine. While some have been released, at least two have been found dead, Kyiv Post reports.

The Vienna-based Organization for Security and Cooperation in Europe has called for Ostrovsky’s immediate release, OSCE Representative on Freedom of the Media Dunja Mijatović said in a statement.

Below is a list of journalists who have been detained in eastern Ukraine.

April 16

Serhiy Lefter, a 22-year-old Ukrainian journalist, was captured. Acquaintances told Reuters they suspect he is being held in Slovyansk. Some reports have speculated he is being held in a basement of the Ukrainian State Security Service building there. While local authorities said they have no witnesses or facts related to Lefter’s disappearance, a representative of Open Dialog Foundation, the nongovernmental organization he was working with, said it last heard from him on April 15.

April 20

Irma Krat, a 29-year-old Ukrainian journalist, was detained after pro-Russian separatists accused her of “war crimes” -- specifically on suspicion of torturing and killing a police officer during the Maidan uprising that ousted the former government of Ukraine. A video posted on the Russian Internet channel Life News shows Irma Krat walking with masked men in combat gear after a news conference in Slovyansk. “They detained me, but they are treating me all right. They will check the reports I've filed and then they'll decide when to let me go," she said.

April 21

Dmitriy Galko, a Belarussan journalist, was captured on Monday by masked gunmen in Slovyansk. French journalist Paul Gogo and Italian Cosimo Attanasio, were grabbed at the same time. The three reporters were later released after a document check, the Associated Press reported. The journalists’ equipment, money and personal documents were confiscated.

April 22

Yevhen Hapych, a Ukrainian journalist, lost contact around 10 a.m. on April 22 in Artemivsk, a town about 30 miles away from Slovyansk. One of his last blog posts on April 21 shows photos of checkpoints in Donetsk.

Ostrovsky, who holds dual American and Israeli citizenship, was also captured on Tuesday. Last seen in the early morning of April 22, he is allegedly being held at a local branch of the Ukrainian Security Service that pro-Russian militiamen seized more than a week ago.

According to Stella Khoraeva, a spokeswoman for pro-Russian insurgents, Ostrovsky’s kidnapping was planned and stems from his “incorrect way” of reporting.

“We knew where he was going and the men manning the checkpoint were told to look out for him,” Khoraeva told the Daily Beast.