The US ambassador in Moscow John Sullivan left Russia on Sunday after completing his diplomatic term there, the embassy said in a statement.
The 62-year-old Sullivan was appointed ambassador to Moscow in December 2019.
“Following his departure, he will retire from a career in public service that has spanned four decades and five US presidents,” the embassy said in a press release.
“Elizabeth Rood will assume duties as Charge d’Affaires at US Embassy Moscow until Ambassador Sullivan’s successor arrives.”
The embassy did not give further details.
Sullivan was assistant secretary of state under the presidency of Donald Trump and held several senior positions in the justice, defence, and commerce ministries throughout his career.
His departure comes at a time when relations between the United States and Russia are at their lowest point since the Cold War.
Since the launch of the Russian offensive in Ukraine at the end of February, the United States has introduced sweeping economic sanctions against Moscow and provided substantial military aid to Kyiv.
The US embassy has also been on the frontline in recent weeks trying to secure the release of its citizens detained in Russia, including basketball superstar Brittney Griner who was sentenced to nine years in jail by a Moscow court in August on a drug charge.