The U.S.-led negotiations have made some progress, but still face fundamental challenges, including over security guarantees to counter future Russian aggression.

Donald Trump has said progress towards a deal to end the war in Ukraine was made in a meeting with Volodymyr Zelenskyy, but the US president warned that several “thorny” issues remained.

Trump and Zelenskyy sitting down face-to-face also underscored the apparent progress made by Trump's top negotiators in recent weeks as the sides traded draft peace plans and continued to shape a prop...