US President Donald Trump’s 50-day pause ahead of possible secondary sanctions on Russia gifts the Kremlin a window to exploit the incremental gains of recent weeks in Ukraine’s east.

On Monday, Trump said that Russia's failure to reach a negotiated settlement with Ukraine within 50 days would lead to his administration imposing a 100% tariff rate on Russian imports as well as what he called "secondary tariffs" on countries that have continued to do business with Moscow.

President Vladimir Putin believes Russia's economy and its military are strong enough to weather any additional Western measures, sources said.