Russian President Vladimir Putin is unlikely to bow to a sanctions ultimatum expiring this Friday from U.S. President Donald Trump, and retains the goal of capturing four regions of Ukraine in their entirety, sources close to the Kremlin told Reuters.

Trump has threatened to hit Russia with new sanctions and impose 100% tariffs on countries that buy its oil - of which the biggest are China and India - unless Putin agrees to a ceasefire in Russia's war in Ukraine.

Putin's determination to keep going is prompted by his belief that Russia is winning and by scepticism that yet more U.S. sanctions will have much of an impact after successive waves of economic penalties during 3-1/2 years of war, according to three sources familiar with discussions in the Kremlin, Reuters reported.