The company's helicopter fell into the Black Sea 70 kilometers (45 miles) off the coast after clipping the side of a drilling platform with its tail rotor.
"There were 20 people on board. Nineteen were killed, and one survived the crash," Valentin Zemlyansky said.
Ukraine's Transport and Communication Minister Yosyp Vinskyi told a news conference that the crash is believed to have been caused by pilot error.
"As far as I know, the helicopter was in good condition and had passed all regular check-ups," he said. "Therefore, the human factor may have been involved."
A special ministerial commission has been set up to investigate the cause of the crash, he added.
The Mi-8, produced at the Mil Moscow Helicopter Plant, is a medium twin-turbine transport helicopter with 24 passenger capacity. It is the world's second most-produced helicopter, and is operated by over 50 countries.
