Russia has accused the UK of "deliberately opting for an escalation of the Ukraine crisis" following confirmation that British-made drones had been used in strikes on targets in Russia.
"In doing so, the United Kingdom is acting as an accomplice and co-perpetrator of the bloody crimes and terrorist attacks," the Russian Embassy to the UK wrote in a statement.
"London's actions will inevitably carry consequences for which it will have to answer," it said, adding that the deeper its involvement in the conflict, "the higher the price it will pay".
In response, a spokesperson for the Ministry of Defence (MoD) told BBC News that Britain stood "shoulder to shoulder" with Ukraine.
"Russia should be in no doubt about the resolve of this Government to stand against Russian aggression, in Ukraine and against the UK and our allies," said the spokesperson in a statement.
The UK, they added, was "committed to providing the equipment Ukraine needs to defend itself against [Russian President Vladimir] Putin's illegal invasion".
The warning comes amid reports of Russia and Ukraine exchanging another barrage of attacks overnight on Monday into Tuesday.
Built by two separate British companies, the drones in question have been used inside Russia in the widespread and successful targeting of military and industrial targets, including refineries and warehouses of the online retailer Wildberries.
Ukraine has repeatedly targeted the company, known as Russia's version of Amazon, and says that seven out of 10 of the largest Wildberries logistics centres have been "disabled".
A military source confirmed to the BBC that UK drones had been used in the attacks, which are said to have caused more than £35bn in economic damage.
Russia launched its full-scale invasion of Ukraine in February 2022 and currently controls approximately a fifth of Ukrainian territory.
Russian foreign ministry spokeswoman Maria Zakharova has said drones using UK components and configurations were used to attack Russian territory, including a fuel depot in the Kamensky District of the Rostov Region.
