Moscow on Monday said it that it could launch strikes at British military targets inside Ukraine and elsewhere if Kyiv's forces used British-supplied long-range missiles to strike Russia.
The statement issued by the Russian foreign ministry came after British Foreign Secretary David Cameron said during a visit to Ukraine that Kyiv "absolutely has the right to strike back at Russia".
He also said that London did not put "caveats" on how Ukrainian forces use weapons supplied by Britain.
The Russian foreign ministry announced it had summoned the UK's ambassador in Moscow, Nigel Casey, and warned him that if Ukrainian forces use British-supplied weapons to strike Russia, Moscow could hit "any UK military facility and equipment on Ukrainian territory and beyond."
"The Ambassador was urged to reflect on the inevitable catastrophic consequences of such hostile steps by London and to immediately refute in the strongest and most unequivocal manner the bellicose provocative statements by the head of the Foreign Office," the statement added.
Russia earlier announced that it was planning new nuclear weapons drills, citing "threats" issued by Western leaders, including French leader Emmanuel Macron and British officials.
Russian forces currently occupy several regions of Ukraine and the Kremlin has claimed to have annexed them and that they are part of Russian territory.