Kostiantyn Liberov/Libkos/Getty ImagesPressure is growing on US President Joe Biden to allow Ukraine to use West-supplied weapons to strike Russian territory.
A number of US allies this week signalled they were open to this possibility.
Russia’s Vladimir Putin has warned of “serious consequences”, especially for what he called “small countries” in Europe.
On Wednesday, US Secretary of State Antony Blinken said Washington’s stance on the matter would “adapt and adjust” based on changing battlefield conditions. He is currently in the Czech capital, Prague, for a meeting of Nato foreign ministers.
White House national security spokesman John Kirby said late on Wednesday that even though US support for Kyiv had evolved, “right now, there’s also no change to our policy”.
Ukraine has been struggling to counter a Russian offensive in the east of the country, while the city of Kharkiv has suffered weeks of deadly attacks, often launched by Russia from military outposts near the Ukrainian border.
Mr Blinken’s statement, during a trip to Europe, followed more direct comments made earlier this week by France’s President Emmanuel Macron, who said Ukraine should be “allowed” to use weapons supplied by the West against military sites on Russian territory – although strictly not on civilian targets.
ReutersMr Macron has for some time advocated for more direct intervention in the Ukraine war – but other Western leaders also appear to be softening to the idea.
German Chancellor Olaf Scholz has remained cautious in public but a spokesman in Berlin said that “defensive action is not limited to one’s own territory, but also includes the territory of the aggressor”.
Last week, Nato chief Jens Stoltenberg told the Economist that the West should allow Ukraine to defend itself by striking military bases in Russia. “Ukraine has the right to defend themselves. And that includes striking targets on Russian territory,” he said.
UK Foreign Secretary Lord Cameron said earlier this month that it was up to Ukraine to decide how to use British weapons, while this week the Polish Deputy Defence Minister said that Ukrainians could use Polish weapons “as they see fit”.
Ukrainian President Volodymyr Zelensky has previously said it was “unfair” for Western countries to impose limits on the use of their weapons, while acknowledging that Ukraine could not risk the support of its partners.
Russia has reacted angrily to the prospect of Western weapons being used against targets on Russian territory.
“In Europe, especially in small countries, they should be aware of what they are playing with,” Vladimir Putin said, noting that many European countries had “small territory” and a “dense population”.
The Russian leader added that responsibility for any strikes inside his country’s territory would lie with Western arms suppliers, even if Ukraine’s forces carried out the strikes.
Some Nato countries remain nervous about the prospect. On Thursday, Italian Prime Minister Giorgia Meloni said she did not think it necessary to hit Russian military bases and urged the West to supply more air defences to Ukraine instead.
However, it is thought Ukraine has already used some Western-supplied weapons for attacks on Russian territory, although it has done so without fanfare.
Latvia’s foreign minister, Baiba Braze, told Ukrainian media that some countries had already provided weapons “without conditions” to Ukraine but that “not everything” was said aloud.
Other countries have been more forthcoming in giving Ukraine permission to use their weapons inside Russia.
The US has already supplied Ukraine with thousands of defensive weapons, tanks and air defence systems.
Since April, it has also sent Ukraine the longest-range version of ATACMS missiles, which can travel up to 190 miles (300km).
Until now, Ukraine has been using drones to attack targets ever further into Russian territory.
Earlier this week it was reported that Ukrainian drones had managed to hit an early-warning radar near the city of Orsk, around 1,500km (932 miles) from the Ukrainian border.