The Obama administration on Wednesday expressed concern over the fate of an American journalist reportedly being detained by pro-Russian militias in eastern Ukraine and urged Moscow to help secure his release.

“We are deeply concerned about the reports of a kidnapping of a U.S. citizen journalist in Slovyansk, Ukraine, reportedly at the hands of pro-Russian separatists,” said State Department spokeswoman Jen Psaki in a statement. “We condemn any such actions, and all recent hostage takings in eastern Ukraine, which directly violate commitments made in the Geneva joint statement.

“We call on Russia to use its influence with these groups to secure the immediate and safe release of all hostages in eastern Ukraine,” she continued. “We have also raised our concerns with Ukrainian officials as they work with local authorities to try to de-escalate the security situation in and around Slovyansk.”

Reports Tuesday said that Simon Ostrovsky, a reporter with Vice News covering the crisis in Ukraine, had been kidnapped by Russian militias in the area who are seeking autonomy from Kiev.

Vice News, in a statement on Tuesday, said they were “aware of the situation” and were in contact with the State Department and other authorities “to secure the safety and security of our friend and colleague, Simon Ostrovsky.”

Pro-Russian groups in Eastern Ukraine, backed by Moscow, have seized government buildings and territory.

The Obama administration has called on Russia to stop backing those groups and to take steps to de-escalate the situation.