London’s decision to supply Kiev with long-range cruise missiles is another step towards a “serious escalation” of the ongoing conflict in Ukraine, the Russian Foreign Ministry said in a statement on Friday. The ministry branded the move as “a very unfriendly step” on the UK’s part, which proves London’s “unprecedented level of involvement” in the conflict.

“Carried away with geopolitical games … the UK is apparently ready to cross any red lines and bring the conflict towards a totally new level when it comes to destruction and casualties,” the ministry’s statement read.

Russia “reserves the right to take any measures deemed necessary to neutralize a threat that may arise from Ukraine’s use of the British cruise missiles,” the ministry said, adding that those behind this “reckless step” and London’s “destructive activities” in general would be to blame for the consequences.

On Thursday, the UK confirmed it was handing several of its Storm Shadow cruise missiles over to Ukraine. The weapons can hit targets over 250km (155 miles) away. British Defence Secretary Ben Wallace claimed it was a “calibrated and proportionate response” by London to the situation in Ukraine.

Washington then indicated on Friday that it was reluctant to follow London’s example. The US has long refused to provide Kiev with longer-range weapons like the ATACMS missiles. In March, Chairman of the Joint Chiefs of Staff General Mark Milley said it was not an option since the move would dwindle the Pentagon’s own stocks.

Some Western officials have reportedly suggested that giving Ukraine the option to attack targets inside Russian territory, which is recognized as such by the US and its allies, would be a major escalation of the conflict.

Kiev has long asked for such longer-range weapons. President Vladimir Zelensky’s top adviser, Mikhail Podoliak, said this week that longer-range missiles could be used to strike Crimea, which Kiev considers an illegally occupied territory. The peninsula joined Russia back in 2014 following a referendum.

Moscow has repeatedly warned Western nations that continued weapons deliveries to Ukraine make them de facto participants of the conflict – something many of them have vehemently denied.

On Thursday, the Kremlin vowed to have an “appropriate answer” to the deliveries of the British missiles.