Two powerful blasts were heard on Thursday in the Russian city of Belgorod, near the border with Ukraine, two witnesses told Reuters.

The blasts were heard in the southern part of the city. It was not immediately clear what caused them and whether there were any casualties or damage.

Russia has in recent days reported what it says are a series of attacks by Ukrainian forces in Belgorod and other southern regions which border Ukraine, and has warned that such attacks raise a risk of significant escalation.

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Ukraine has not directly accepted responsibility but has described the incidents as payback and “karma” for Russia, nine weeks after it invaded its neighbour.

Russian Foreign Ministry spokeswoman Maria Zakharova accused the West earlier on Thursday of openly calling on Kyiv to attack Russia, and warned it not to “test our patience”.