President Donald Trump called for a 30-day ceasefire between Russia and Ukraine to pave the way for talks on a lasting peace agreement, and threatened to impose further sanctions if a truce is violated.

U.S. President Donald Trump called on Thursday for a 30-day unconditional ceasefire between Russia and Ukraine, warning that Washington and its partners would impose further sanctions if the ceasefire is not respected.

Kurt Volker, Trump's Ukraine adviser in his first term and former U.S. Ambassador to the NATO military alliance, told Reuters the U.S. leader had started his second term with a challenge to Russian President Vladimir Putin to secure peace either "the easy way or the hard way".