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.

Russian President Vladimir Putin said his forces may use a new missile again after targeting Ukraine in retaliation for Kyiv’s use of American and British-made weapons on Russian territory this week.

"Bomb shelters will not help," former President Dmitry Medvedev said on Sunday, in a stark warning to the West over Russia's newest missile.