Russian energy company Gazprom said it has "stopped supplying un-paid-for gas to Ukraine" this morning, according to reports in Russian media.
Gazprom said Ukraine has failed to pay for its gas supplies.
A Gazprom spokesperson told ITV News the company will now require all payments to be made in advance.
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An unidentified male suspect is alleged to have wounded at least five people, two seriously, in an attack in the city of Schaffhausen.
Donald Trump's son-in-law has denied any improper conduct during four contacts with Russians during and after the presidential election.
Police are appealing for witnesses after Sunday night's incident, which is not being treated as terror-related.