Three U.S. officials confirmed the authenticity of the letter and its contents.
Foreign Policy first reported Friday on U.S. agencies having intelligence about a Russian “kill list,” and the Washington Post first reported on the letter on Sunday.
The letter noted that U.S. Secretary of State Antony J. Blinken had raised the human rights concerns to the United Nations Security Council when he addressed that body on Thursday. “In particular, he stated that the United States has information that indicates Russia will target specific groups of Ukrainians,” the letter said.
In that session, Mr. Blinken told Russian officials they could prove their peaceful intentions to the world by not invading Ukraine and addressing their grievances through diplomacy instead. Mr. Blinken plans to meet Sergey V. Lavrov, the foreign minister of Russia, in Europe this Thursday, unless Russia invades Ukraine first.
President Biden and Mr. Blinken have said U.S. intelligence indicates Russian President Vladimir V. Putin has already decided to invade. In recent weeks, Mr. Putin has amassed as many as 190,000 troops around Ukraine. Russia-backed insurgents in the east have increased their artillery shelling of Ukrainian military forces in recent days.
Mr. Putin invaded parts of Ukraine in 2014 and annexed the country’s Crimean Peninsula. Mr. Biden has promised to impose harsh economic sanctions on Russia if Mr. Putin carries out another invasion.