Ukrainian President Petro Poroshenko has 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, including the interior minister, have welcomed the publication and have accused the journalists of accessory to terrorism.

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 from the lists made "criminal things."

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