Russia warned Britain on Monday that if British weapons were used by Ukraine to strike Russian territory, Moscow could hit back at British military installations and equipment inside of Ukraine and elsewhere.

British Ambassador Nigel Casey was summoned to the foreign ministry for a formal protest after Foreign Secretary David Cameron said last week that Ukraine had the right to use British weapons to strike Russia.

Russia's foreign ministry said the Cameron remarks recognized that Britain was now de facto a part of the conflict and contradicted an earlier assurance that long-range weapons given to Ukraine would not be used against Russia.

"Casey was warned that in response to Ukrainian attacks on Russian territory with British weapons, any British military facilities and equipment on the territory of Ukraine and abroad" could be targeted, the foreign ministry said.

The ministry said it considered Cameron's remarks a serious escalation.

"The Ambassador was called upon to reflect on the inevitable catastrophic consequences of such hostile steps by London and immediately refute the belligerent provocative statements of the head of the Foreign Office in the most decisive and unambiguous way."

Cameron, during a visit to Kyiv last week, told Reuters that Ukraine had a right to use the weapons provided by Britain to strike targets inside Russia, and that it was up to Kyiv whether or not to do so.

Reuters could not immediately reach British officials for comment on Monday.