Russia's President Vladimir Putin and U.S. President Donald Trump talk during a bilateral meeting at the G20 leaders summit in Osaka, Japan, June 28, 2019. (REUTERS/Kevin Lamarque/File Photo)

Trump has also paused military aid and intelligence sharing with Ukraine to pressure Kyiv to accept a ceasefire deal.

"Based on the fact that Russia is absolutely 'pounding' Ukraine on the battlefield right now, I am strongly considering large-scale Banking Sanctions, Sanctions, and Tariffs on Russia until a Cease Fire and FINAL SETTLEMENT AGREEMENT ON PEACE IS REACHED," Trump said on his social media platform. 

The US Treasury Department is looking at possible sanctions on Russian oil majors and oilfield service companies, a source familiar with the matter said, deepening steps already taken by former President Joe Biden's administration in January. 

Ukrainian President Volodymyr Zelenskiy, has called for a truce covering air and sea.

Moscow has rejected the idea of a temporary truce, which has also been proposed by the UK and France, and said it would never let peacekeepers from NATO countries into Ukraine, after the two countries suggested a European force could police any permanent settlement.