Donald Trump has said the US could play a role “by air” in a postwar security guarantee for Ukraine, as he warned Vladimir Putin that he would face a “rough situation” if he did not co-operate on a peace deal.

Ukraine and its European allies have been buoyed by Trump's promise during a summit on Monday of security guarantees for Kyiv, but many questions remain unanswered. Officials told Reuters that the Pentagon is carrying out planning exercises on the support Washington could offer beyond providing weapons.

U.S. President Donald Trump said on Tuesday the United States would not put troops on the ground in Ukraine but might provide air support as part of a deal to end Russia's war in the country. Alex Cohen has more.