A dramatic rise in Ukrainian attacks on Russian oil refineries has sent gasoline prices in Russia to record highs, despite the government banning petrol exports to cope with the crunch.

NATO allies and Ukraine are working together to make sure security guarantees for Ukraine are at such a robust level that Russia will never try to attack again, NATO chief Mark Rutte said on Friday, adding that Europe and the United States would be involved in providing them.

U.S. President Donald Trump renewed a threat to impose sanctions on Russia on Friday if there is no progress toward a peaceful settlement in Ukraine in two weeks, showing frustration at Moscow a week after his meeting with Russian President Vladimir Putin in Alaska.