Public joint-stock company Ukrtatnafta (Kremenchuk, Poltava region) has set up an ad hoc commission to investigate the blast at Kremenchuk oil refinery, head of Ukrtatnafta's public relations service Serhiy Bilenky told reporters on Monday.

He said that an explosion occurred at a facility which was not operating.

"This is an accident during welding works. No fire or flame was seen," he said.

A contracted welder was killed. He fell from a height of around 12 meters from the force of the blast. Another worker was in a state of shock.

An employee of Ukrtatnaftaservice (Kremenchuk) was killed after a methanol vapor blast, the Emergencies Service of Ukraine reported.

The Interior Ministry in Poltava region said that methanol vapor blasted occurred in a empty tanker during welding works.

Prosecutor General's Office in Kremenchuk opened criminal proceedings under Part 2 of Article 272 of the Criminal Code of Ukraine (violation of safety rules during major hazard works).