Russia has accused Britain of escalating the Ukraine war and says weapons it has supplied will be targeted.
An official from the invading country made the warning after the UK delivered Starstreak missiles to Ukraine.
A video has emerged of what appears to be one of the high-tech munitions being used to down a Russian helicopter.
Defence Secretary Ben Wallace has said that more weapons will be sent to Kyiv to aid Ukraine in its efforts to repel Russia.
The pledge, which was made after a conference held by military donors to the country, has not been met warmly by Russian ambassador Andrey Kelin.
Mr Kelin told TASS news agency: "All arms supplies are destabilising, particularly those mentioned by Wallace.
"They exacerbate the situation, making it even bloodier. Apparently, those are new, high-precision weapons.
"Naturally, our armed forces will view them as a legitimate target if those supplies get through the Ukrainian border."
Since Russia invaded Ukraine the UK has been providing it with military aid, including anti-tank weapons and the Starstreak.
The latter is the UK’s most advanced manned portable missile system and hits targets with three kinetic darts.
A video showing the tail of a Mi-28N helicopter being snapped off has been verified, reported the Times, with a Ministry of Defence source saying it showed a Starstreak in action in Ukraine.
The source also said that the anti-air missile system has been used in Ukraine for almost a week.
Mr Wallace hosted a conference of 35 nations helping Ukraine this week.
He said that "more lethal aid" would go to the country. and that longer range artillery would be provided, along with anti-ship missiles.
Mr Kelin warned against supplying more arms, saying that "wrong decisions of this kind are very dangerous, because they are aimed at fuelling the conflict".
He added: "They reveal the desire to do us as much harm as possible.
He went on to claim that supplying more weapons will serve to fuel the idea "that there's no need for negotiations at this point".
"This is the position of an ostrich, an attempt to hide your head in sand in a fit of powerlessness and blind rage."
Kelin also looked to counteract claims that Russia is being pushed back by Ukrainian forces, suggesting that the West had been duped by unreliable intelligence.
"I have a feeling that London’s perceptions of what is going on in Ukraine from the military point of view are formed from overly positive reports of the Ukrainian Defence Ministry and the leadership of Ukraine," he continued.
"If we look at maps that are being published by papers and magazines here, they rely exclusively on Ukrainian sources.
"They still believe that the Azov battalion is about to liberate Mariupol, that the people’s militia forces have made no progress at all in the Lugansk region."
The ambassador may have been responding to comments Mr Wallace made yesterday, when he claimed Vladimir Putin "is now a man in a cage he built himself".
As the Russian war against Ukraine entered day 37, the Defence Secretary said Russia's president no longer bore the "force" he used to.
In an interview with Sky News, he said: "President Putin is not the force he used to be. He is now a man in a cage he built himself.
"His army is exhausted, he has suffered significant losses.
"The reputation of this great army of Russia has been trashed.
"He has not only got to live with the consequences of what he is doing to Ukraine, but he has also got to live with the consequences of what he has done to his own army.
"We have seen it before. It always gets worse. It goes for more civilian attacks, more civilian areas."
The Chief of the Defence Staff earlier expressed similar sentiments.
Admiral Sir Tony Radakin said Russia's bid to take all of Ukraine during its invasion looks to have "fallen apart" as Mr Putin's troops retreat.
The head of Britain's armed forces said the Russian leader had been "misled" about the effectiveness of his country's armed forces, with "early indications" suggesting Moscow was withdrawing troops - a move that has opened them up to counter attacks by Ukrainian defenders.
In a speech and follow-on question-and-answer session at an Institute for Government (IfG) event, the Chief of the Defence Staff said Mr Putin was a "weaker and more diminished figure today" than he was before the invasion started on February 24.
He announced that the UK was "incredibly cautious" about believing Russian claims of ground troops withdrawing from Kyiv but said there did appear to be signs the Kremlin was preparing to focus its efforts on the east and south of Ukraine.
