The six U.S. service members killed in an Iranian drone attack over the weekend were working in a tactical operations center in Kuwait that offered little protection from overhead strikes, according to imagery, experts and officials.

They are the only U.S. troops known to have died in retaliatory strikes since the operation in Iran began Saturday. At least 10 American military outposts have been hit, along with bases belonging to France and Britain, according to a Washington Post review of satellite images and videos.