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.

Many of the drones aren’t particularly fast or high-tech, but they are cheap enough for the Kremlin to launch more than 700 in one night, in an effort to overwhelm Ukraine’s air defenses. Here’s what we know.

President Donald Trump again on Monday expressed frustration with Russian counterpart Vladimir Putin as Russian strikes on Ukraine continued despite White House efforts to broker a peace deal between the warring neighbors.