Putin Lowers Nuclear Weapons Threshold After U.S. Allows Ukraine to Use Missiles Against Russia

President Vladimir V. Putin on Tuesday lowered Russia’s threshold for the use of nuclear weapons, a long-planned move whose timing appeared designed to show the Kremlin could respond aggressively to Ukrainian strikes on Russian territory with American long-range missiles.

The decree signed by Mr. Putin implemented a revised version of Russia’s nuclear doctrine that Mr. Putin described in televised remarks in September. But the timing was clearly meant to send a message, coming just two days after the news that President Biden had authorized the use of U.S.-supplied long-range missiles by Ukraine for strikes inside Russia.

Asked whether Russia could respond with nuclear weapons to such strikes, Dmitri S. Peskov, Mr. Putin’s spokesman, repeated the new doctrine’s language that Russia “reserves the right” to use such weapons to respond to a conventional-weapons attack that creates a “critical threat” to its “sovereignty and territorial integrity.”

Russia’s Ministry of Defense later announced that Kyiv had used the long-range ballistic missiles known as the Army Tactical Missile System, or ATACMS, in a pre-dawn attack on an ammunition depot in southwestern Russia. A senior American and a senior Ukrainian official, both of whom spoke on the condition of anonymity to discuss ongoing operations, confirmed that ATACMS were used.

The White House played down Mr. Putin’s new doctrine. In a statement, issued by a spokesperson for the National Security Council, the White House noted that it had observed “no changes to Russia’s nuclear posture.”

The new doctrine, published Tuesday on the Kremlin website, differs from the previous iteration in at least two important ways that show how Mr. Putin is trying to use the threat of his nuclear arsenal to deter the United States from further supporting Ukraine.