KIEV, Ukraine (AP) — Ukrainian President Petro Poroshenko on Friday condemned the leak of the names and contact information for thousands of journalists who have reported from rebel-controlled eastern Ukraine.

The May publication by hackers from a group called Myrotvorets has raised concerns about the safety of the journalists, many of them from international media organizations.

Some Ukrainian officials however, including the interior minister, have welcomed the publication of the data, accusing the journalists of being accessories to terrorism.

Several journalists have reported threats from unknown people who called on their phones or sent messages to the email addresses listed in the publication.

Ambassadors to Ukraine from the Group of Seven countries on Thursday expressed concern about the publication.

Poroshenko on Friday told reporters that the publication was a "big mistake" and called for a probe into the leak. Poroshenko, however, called on journalists not to write "negative articles" about Ukraine and said some Russian reporters on the lists made "criminal things." He did not elaborate.

"I would like to offer guarantees to journalists that there are no threats to you," he said.

The hackers said they had gained access to computers used by the Russia-backed separatists to register journalists working in the conflict zone and felt it was necessary to publish the list "because these journalists collaborate with fighters from terrorist organizations."