U.S. President Donald Trump’s special envoy Keith Kellogg said in Kyiv on Monday that officials are “working very, very hard” on efforts to end the three-year war between Russia and Ukraine, as a lack of progress fuels doubts about whether a peace settlement could be on the horizon.

The fast-moving developments in Trump's near-back-to-back summits with the heads of Russia, Ukraine and European powers have highlighted a pair of repeated sticking points.