Kathimerini correspondent Costas Onishenko was one of several journalists attacked by militants outside a Ukrainian air force base in Sevastopol, Crimea, late on Friday.
It is not clear who assaulted the group of journalists, which included a Ukrainian television crew, but pro-Russian militants had been accused of similar attacks in the previous days.
Onishenko and others had been covering a reported attack on the base by pro-Russian forces, who eventually left without any shots being fired.
The assailants stole Onishenko’s passport and other items, leaving him only with his mobile phone.
The Associated Press reported on Saturday that armed men in the Crimean capital Simferopol had seized equipment from one of its crews.
“Self-styled Crimean self-defense groups are harassing pro-Ukrainian protesters, journalists and human rights monitors with complete impunity,” said John Dalhuisen, Amnesty International’s Europe and Central Asia director.