The US Secretary of State, Marco Rubio, has told reporters in Switzerland that talks about US proposals to end the war in Ukraine have been "very meaningful" - calling it the "best day" for the peace process since President Trump returned to office. American, European and Ukrainian officials have been meeting to go over the plans, which have been criticised as being favourable to Russia. Earlier, Mr Trump posted a message on social media, accusing Ukraine of showing "zero gratitude" for Washington's attempts to end the conflict.