Vice journalist Simon Ostrovsky has been taken by militia in Eastern Ukraine, Mashable has learned.

The reporter for Vice News, who has been filing a series of compelling video dispatches from Ukraine since early March, was "taken" in Sloviansk, Russian media outlet gazeta.ru reports (translation by The Interpreter):

The "People's mayor" of Slavyansk, Vyacheslav Ponomarev, said that the militia has taken the American journalist, Simon Ostrovsky, hostage, reports a correspondent for Gazeta.ru, Ponomarev announced this during a press conference at the House of Culture in Slavyansk.

Sloviansk's self-appointed "People's Mayor," Vachislav Ponomaryov, reportedly held a press conference where he claimed to call Ostrovsky's parents to assure them that their son was okay, the outlet reports. "Nobody abducted him, nobody is holding him hostage, he's with us now in at the SBU, preparing material and working," Ponomaryov said, raising the remote possibility that Ostrovsky is merely embedded with the militia.

But Roland Oliphant, Moscow correspondent for The Telegraph, says the mayor and his press secretary confirmed the reporter was "in custody" at the press conference. "But very little further information so far," he adds.

The mayor of Slavyansk & his press sec have confirmed @SimonOstrovsky is in custody in Slavyansk. I was at the presser. — Roland Oliphant (@RolandOliphant) April 22, 2014

In a statement sent to Mashable and posted on its website, a Vice News spokesman said the media organization is in touch with the U.S. State Department and working to secure their reporter's safety: "VICE is aware of the situation and is in contact with the United States State Department and other appropriate government authorities to secure the safety and security of our friend and colleague, Simon Ostrovsky."

Vice News also tweeted a similar statement shortly after noon on Tuesday: "We are aware of @SimonOstrovsky's situation and are working to ensure the safety and security of our friend and colleague."

We are aware of @SimonOstrovsky's situation and are working to ensure the safety and security of our friend and colleague. — VICE News (@vicenews) April 22, 2014

Ponomaryov's militia has, in the past, held journalists against their will — most recently capturing Imra Krat and parading her before reporters in a blindfold.

Ostrovsky's last two tweets, sent April 21, are about the "mayor" threatening to remove an Associated Press journalist from a press conference. He has not tweeted since Monday's press conference.

His most recent video dispatch was posted April 20.

"Sloviansk pro-Russia 'mayor' threatens to throw journalist out for "provocative" question about former mayor being held under guard," Ostrovsky last tweeted while covering the press conference. "Now he's not letting reporters leave the press conference: 'you'll go as you came in. In a group.' That's one way to guarantee coverage."

Sloviansk pro-Russia 'mayor' threatens to throw journalist out for "provocative" question about former mayor being held under guard — Simon Ostrovsky (@SimonOstrovsky) April 21, 2014

Now he's not letting reporters leave the press conference: "you'll go as you came in. In a group." That's one way to guarantee coverage. — Simon Ostrovsky (@SimonOstrovsky) April 21, 2014

Update April 22, 2:45 p.m. ET: OSCE Representative on Freedom of the Media Dunja Mijatović called for the immediate release of the detained journalist. “I remain deeply concerned about the ongoing negative pattern in relation to journalists’ safety in Ukraine” Mijatović said. “I call on all those responsible to stop harassing and attacking journalists and let them do their job. Simon Ostrovsky should be released immediately.” A U.S. State Department spokesperson also reportedly mentioned a "range of reports about journalists that have been kidnapped and detained in Ukraine," and condemned the taking of hostages.

Update April 22, 4:20 p.m. ET: Journalist Graham W Phillips visited Sloviansk's city hall to inquire of Simon's whereabouts — and was met by masked men with automatic weapons. Later, though, he was invited inside to eat with the acting mayor, and says he is "doing what poss to get Simon out." That includes, for the vegetarian Phillips, eating meat.