US officials say President Biden has given the green light for Ukraine to use long range missiles supplied by Washington to strike deep inside Russia.
Washington had previously refused to allow such strikes with US-made ATACMS missiles because it feared they would escalate the war.
The major policy reversal comes two months before President Joe Biden hands over power to Donald Trump, whose election has raised fears over the future of US support for Kyiv.
Ukraine has been using ATACMS on Russian targets in occupied Ukrainian territory for more than a year.
American munitions and hardware are already being used inside Russia – in the Kursk border region, according to local reports.
But the US has never allowed Kyiv to use the ATACMS inside Russia – until now.
Ukraine had argued that not being allowed to use such weapons inside Russia was like being asked to fight with one hand tied behind its back.
The change in policy reportedly comes in response to the recent arrival of North Korean troops to support Russia in the Kursk region, where Ukraine has occupied territory since August.
Also, Donald Trump’s imminent return to the White House is raising fears over the future of US support for Ukraine, and President Biden is apparently keen to do all he can to help in the little time he has left in office.
Strengthening Ukraine's hand militarily – so the thinking goes - could grant Ukraine leverage in any peace talks that may lie ahead.
Ukrainian President Volodymyr Zelensky has not yet confirmed the move. But he said on Sunday: "Strikes are not made with words ... The missiles will speak for themselves."
The Army Tactical Missile System is a surface-to-surface ballistic missile capable of hitting targets at up to 300km (186 miles) and it is their range that makes them particularly important for Ukraine.
Built by the defence manufacturer Lockheed Martin, they’re fired from either the tracked M270 Multiple Launch Rocket System (MLRS) or the wheeled M142 High Mobility Artillery Rocket System (HIMARS). Each missile costs around $1.5m (£1.2m).
ATACMS (pronounced “attack-‘ems”) are fuelled by solid rocket propellant and follow a ballistic path into the atmosphere before coming back down at a high speed and high angle, making them difficult to intercept.
They can be configured to carry two different types of warhead. The first is a cluster fitted with hundreds of bomblets designed to destroy lighter-armoured units over a wide area. These might include parked aircraft, air defences and concentrations of troops. Cluster warheads, while useful, risk leaving behind unexploded bomblets which pose a risk long after the fighting has stopped.
The second type is a single warhead, a 225kg high explosive variant of which is designed to destroy hardened facilities and larger structures.
ATACMS have been around for decades. They were first used in the Gulf War of 1991.
The US Army is replacing it with the next-generation Precision Strike Missile, a faster, slimmer weapon that can go out to 500km. There is no suggestion Ukraine will be getting these.
The Biden administration had for months refused to authorise Ukraine to hit Russia with long-range missiles, fearing escalation of the conflict.
Vladimir Putin has warned against allowing Western weapons to be used to hit Russia, saying Moscow would view that as the “direct participation” of Nato countries in the war in Ukraine.
“It would substantially change the very essence, the nature of the conflict,” Putin said in September. “This will mean that Nato countries, the USA and European states, are fighting with Russia.”
Russia has set out “red lines” before. Some, including providing modern battle tanks and fighter jets to Ukraine, have since been crossed without triggering a direct war between Russia and Nato.
Kurt Volker, a former US ambassador to Nato, said: “By restricting the range of Ukraine’s use of American weapons, the US was unjustifiably imposing unilateral restrictions on Ukraine’s self-defence."
He added that the decision to limit the use of ATACMS was "completely arbitrary and done out of fear of ‘provoking’ Russia."
“However, it is a mistake to make such a change public, as it gives Russia advance notice of potential Ukrainian strikes.”
