Diplomats are expelled from Moscow and Russian offices are shut down in the United States.
US President Donald Trump promised better relations with Moscow than under his predecessor Barack Obama, then quickly became surrounded by scandal and allegations that Russian computer hackers helped him win the race for the White House.
Russia denied election meddling, the president is being investigated for treason, he has sacked some of his closest aides, and Congress has imposed new Russian sanctions.
Trump said last month relations were at an “all-time and very dangerous low”. That relationship is even worse now.
Russian leaders say the US order to shut down diplomatic offices in three American cities is a “blunt act of hostility”.
That followed Russia ordering hundreds of US diplomats to leave Moscow.
What is behind the tit-for-tat tension?