Joe Biden has given Ukraine the green light to use US-supplied long-range missiles to hit targets in Russia for the first time.
According to the New York Times, the American president has signed off on the use of ATACMS missiles in the Kursk region.
His decision will raise expectations that Britain, the US and France could quickly authorize Kiev to use Storm Shadow missiles in the same way.
Volodymyr Zelensky, the Ukrainian president, has for months urged Britain, the US and France to allow him to attack targets in Russia.
Sir Keir Starmer is known to be in favour, as is Emmanuel Macron, the French leader. But Mr. Biden, who has a veto because the guidance chips in the missiles are American-made, has so far been reluctant to move forward.
Kursk, which borders Ukraine, has seen heavy fighting since Ukrainian forces seized several towns in the region.
Biden's decision is said to have been prompted by the arrival of North Korean troops in Kursk. Pyongyang will send as many as 100,000 soldiers, Bloomberg reported on Sunday.
Joe Biden, the US president, and Volodymyr Zelenskyy, the Ukrainian president, disagree on the use of weapons – Kevin Lamarque/Reuters
He also responded to fears that Moscow's strike force could push Ukraine from its foothold on Russian territory.
Kiev has advocated using long-range missiles so it can attack Russian supply lines and command centers, as well as air bases used to launch fighter jets that fire glide bombs at its troops.
Biden previously allowed Ukraine to fire the 80-kilometer Himars missiles across the border, but had prevented the use of the 300-kilometer ATACMS missiles for fear of an escalation of the war.
