WASHINGTON: US President Joe Biden has given the green light for Ukraine to use long-range missiles supplied by the US to strike Russia.
A US official has confirmed the move, a major change of US policy, to the BBC's US partner CBS.
For months, Ukraine's President Volodymyr Zelensky has been urging that the restrictions on the missiles, known as ATACMS, be lifted - allowing Kyiv to strike outside its own borders.
On Sunday he reacted to the reports, saying "such things are not announced, missiles speak for themselves".
Russian President Vladimir Putin haspreviously warned Western nationsagainst such a move, saying it would represent the Nato military alliance's "direct participation" in the Ukraine war.
He was yet to comment on Sunday's reports although other senior Kremlin politicians described it as a serious escalation.
Washington’s decision on ATACMS is couched in terms of being limited to the defence of Ukrainian forces inside Russia's Kursk region, where Kyiv launched a surprise incursion in August.
In effect, the Biden administration is telling Ukraine that it will support its efforts to hold onto the small chunk of Russian territory it currently occupies, as a powerful bargaining chip for any possible negotiations in the future.
Serhiy Kuzan, chairman of the Kyiv-based Ukrainian Security and Cooperation Centre, told the BBC that Joe Biden's decision was "very important" to the country.
"It’s not something that will change the course of the war, but I think it will make our forces more equal.”
Unnamed US officials have told the New York Times and the Washington Post that Biden's approval of Ukraine's use of the ATACMS came in response toRussia's decision to allow North Korean soldiers to fight in Ukraine.
Kuzan said Sunday's decision came just in time to counter the expected start of a major assault by Russian and Korean troops, designed to dislodge Ukrainian forces from Russia's Kursk region. The assault is expected within days.
Ukraine has previously estimated that there are 11,000 North Korean soldiers in Kursk.
There is another knock-on consequence. President Biden’s decision will finally enable Britain and France to grant Ukraine permission touse long-range Storm Shadow missiles inside Russia.
Neither the UK nor France has yet responded to Biden's decision.
ATACMS can reach up to 300km (186 miles) and are tough to intercept due to their high speed.