President of Ukraine Petro Poroshenko says about 23 Russian servicemen who are kept prisoners in places of detention in Ukraine.

"Some 23 Russian soldiers and officers who are kept in Ukrainian prisons and are also called "they are not there." This is the evidence of the presence of the Russian Federation [Russian servicemen in Donbas]," Poroshenko said at a joint briefing with German Chancellor Angela Merkel in Berlin on Tuesday.

"Russia has refused to acknowledge the involvement of its army in the aggression against Ukraine in Donbas, the chemical attack in Syria, and the poisoning incident in Salisbury, the UK," Poroshenko said. "The world no longer accepts the slogan 'They're not there'; no one believes it," he said.