U.S. President Donald Trump says he has called Russian President Vladimir Putin and begun to arrange a meeting between Putin and Ukrainian President Volodymyr Zelenskyy, a critical step toward bringing a possible end to Russia's war on Ukraine.

U.S. President Donald Trump told President Volodymyr Zelenskiy on Monday that the United States would help guarantee Ukraine's security in any deal to end Russia's war there, though the extent of any assistance was not immediately clear.

Ukraine will promise to buy $100bn of American weapons financed by Europe as part of a deal to obtain US guarantees for its security after a peace settlement with Russia, according to a document seen by the Financial Times.