European leaders have dismissed Vladimir Putin’s warning that the west would be directly fighting Russia if it allowed Kyiv to strike Russian territory with western-made long-range missiles.

The US and UK are discussing, in conjunction with other allies, allowing Kyiv to strike military targets inside Russia with Storm Shadow missiles, which can hit targets up to 155 miles (250km) from their launch site.

The Russian president said on Thursday that any western decision to let Kyiv use longer-range weapons against targets inside Russia would put Nato “at war” with Moscow.

“This would in a significant way change the very nature of the conflict,” Putin said, adding that Russia would take “appropriate decisions based on the threats that we will face”.

The Kremlin’s calculus remains unclear as Russia – a nuclear power – continues fighting in Ukraine and collaborating with countries such as Iran, which western capitals have accused of providing Moscow with ballistic missiles.

But European leaders have downplayed the significance of the Russian leader’s threats.

“It is necessary to take all events in Ukraine and on the Ukrainian-Russian front very seriously, but I would not attach excessive importance to the latest statements from president Putin,” said the Polish prime minister, Donald Tusk. “They rather show the difficult situation the Russians have on the front,” he added.

The British prime minister, Keir Starmer, also responded to Putin’s threats, telling reporters: “Russia started this conflict. Russia illegally invaded Ukraine. Russia can end this conflict straight away. Ukraine has the right to self-defence.”

Starmer, who will meet the US president, Joe Biden, in Washington on Friday, said the UK had provided “training and capability” to help Ukraine repel the Russian invasion and he was visiting Biden partly because “there are obviously further discussions to be had about the nature of that capability”.

On Friday, the Kremlin spokesperson, Dmitry Peskov, said there was no doubt that the Russian president’s message had reached those it was intended for.

But in Nato policy circles, there was a sense that Putin’s comments should not be taken at face value.

“I think that the Russian regime, and especially the president, usually does this when he doesn’t know how to respond – it’s usually just rhetoric,” said Peter Bátor, a defence policy expert who until recently served as Slovakia’s ambassador to Nato.

“If we learn one lesson in this Russian aggression against Ukraine, it’s that we should not listen to Putin. He has been lying to us all the time,” the former ambassador said.

A senior diplomat from eastern Europe, who spoke on condition of anonymity, argued there should be no restrictions on how weapons were used. “According to international law, one country is allowed to defend its sovereignty and territorial integrity against the aggression of another how it sees fit,” the diplomat said. “The simple fact that military support to Ukraine comes with limitations is actually the problem.”

The source said: “We see more Russian attacks on civilian Ukrainian infrastructure, more hybrid actions against allies and more drones and missiles entering Nato airspace on the eastern flank – Latvia, Poland, Romania.”

The diplomat added: “Putin threatened the west before and he will continue to do so as long as these threats have an impact.”