Officials initially resisted such a move, citing escalation concerns and uncertainty over how Putin would respond. Some of those officials, including in the White House, the Pentagon and the State Department, feared lethal retaliation on U.S. military and diplomatic personnel and attacks on NATO allies.

A decree signed by the Russian leader, though long planned, came days after President Biden authorized the use of U.S.-supplied missiles by Ukraine for strikes inside Russia.

On Thursday, Moscow used a medium-range ballistic missile against Kyiv that followed Ukraine's use of U.S.- and British-supplied long-range ATACMS and Storm Shadow missiles to strike targets in Russia for the first time.

Russia's Dmitry Medvedev warned of nuclear war if the U.S transfers nuclear weapons to Ukraine: "The consequences are obvious."