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.

U.S. and Russian government officials discussed several energy deals on the sidelines of negotiations this month that sought to achieve peace in Ukraine, according to five sources familiar with the talks.