A Ukrainian warplane has for the first time fired a weapon that struck a target inside Russia, a Ukrainian military source has told Sky News.
The source said a "Russian command node" was hit on Sunday in the area of Belgorod, western Russia.
Belgorod is close to the border with northeastern Ukraine.
It was not immediately clear what type of munition was used in the attack, including whether or not it had been a Western weapon.
The United States and France recently said the Ukrainian armed forces were permitted to use their arms to strike military targets inside Russia - from where Russian forces are launching attacks against Ukraine.
Under new guidance approved by President Joe Biden, American munitions can be used on Russian soil to help defend the city of Kharkiv in northeastern Ukraine.
Lord Cameron, the UK foreign secretary, has been less specific, merely saying it was up to Ukraine to decide how they use British weapons - such as Storm Shadow cruise missiles that can be fired by Ukrainian jets.
