Britain is expected to supply Storm Shadow missiles for use by Ukraine on targets inside Russia, now that the US president, Joe Biden, has agreed to do the same for the similar American long-range Atacms weapon.

Keir Starmer, the prime minister, said at the G20 summit that the UK recognised it needed to “double down” on its support for Ukraine, while diplomatic sources briefed they expected other European countries to follow the US lead.

The prime minister said that, while he was “not going to get into operational details”, he recognised the need to do more to help Ukraine, whose electricity network was seriously damaged by a wave of Russian bombing on Sunday.

“I’ve been really clear for a long time now, we need to double down. We need to make sure Ukraine has what is necessary for as long as necessary, because we cannot allow Putin to win this war,” the prime minister said.

Russia, however, accused the west of escalation and said that Biden risked adding “fuel to the fire” in Ukraine, and while Donald Trump remained silent on the issue, his son Don Jr accused the military industrial complex of wanting to get “world war three going”.

Storm Shadow missiles have a range of about 250km (155 miles), similar to the US Atacms, and have in the past been given to Kyiv by the UK and France to strike targets inside Ukraine’s internationally recognised borders.

But the US retained an effective veto on their use because it supplies a guidance system and repeated lobbying by the UK had failed to shift the US position, which has only begun to soften after the election victory of Donald Trump earlier this month.

Ukraine wants to be able to strike barracks, fuel and logistics hubs, and airbases deeper inside Russia to blunt Moscow’s relentless attacks on their country. Russia, by contrast, is able to strike targets anywhere in Ukraine.

Biden had refused to allow permission for long-range missiles to be used inside Russia for years but finally relented on Sunday, and said that Ukraine could use Atacms missiles to try to halt an expected counter-offensive by an estimated 50,000 Russian and North Korean forces in Kursk.

Ukraine had also become increasingly exasperated with Britain on the issue of long-range missiles, complaining earlier this month that not only had there been no progress on their use inside Russia but that the UK had stopped supplying them at all.

Vladimir Putin’s spokesperson, Dmitry Peskov, accused the US of escalation. “It is clear that the outgoing administration in Washington intends to take steps to continue to add fuel to the fire and to further inflame tensions around this conflict.” He added: “This decision is reckless, dangerous, aimed at a qualitative change, a qualitative increase in the level of involvement of the United States.”

Peskov said Putin had expressed his position clearly in September when the Russian leader warned that the move to let Kyiv use longer-range weapons against targets inside Russia would mean Nato would be directly “at war” with Moscow.

Putin had said Moscow would “take the appropriate decisions based on the threats that we will face” and previously suggested Moscow could supply long-range weapons to other countries with the aim of attacking western targets.

Jean-Noël Barrot, France’s foreign minister, said that the country’s president, Emmanuel Macron, had already said Paris was open to consider greenlighting the use of its missiles to strike on Russian soil. Storm Shadow missiles are manufactured by MBDA, a company with UK, French and Italian shareholders.

“We openly said that this was an option that we would consider if it was to allow Ukraine to strike targets from where Russians are currently aggressing Ukrainian territory,” Barrot told reporters in Brussels.

The German foreign minister, Annalena Baerbock, described Biden’s decision as “important” and “essential”. She said in Brussels: “The decision from the American side, and I would like to emphasise that this is not a rethink but an intensification of what has already been delivered by other partners, is so important at this moment.”

A German government spokesperson said, however, that Germany was sticking with its decision not to supply Kyiv with long-range Taurus missiles. The decision by the chancellor, Olaf Scholz, to withhold its most powerful missile has been a significant point of contention in Germany.

But there was also criticism in Europe from Hungary, seen as Putin’s closest EU ally.

“The pro-war mainstream has launched its last, desperate attack on the new reality,” the Hungarian foreign minister, Péter Szijjártó, wrote on Facebook, referring to the recent victory of Donald Trump.

“The hawkish politicians ousted from power refuse to take note of the will of the people. This is not only undemocratic, but also extremely dangerous,” Szijjártó added.

Trump’s team are yet to officially comment on Biden’s move. The president-elect’s son Don Jr criticised the decision, writing on X: “The military industrial complex seems to want to make sure they get world war three going before my father has a chance to create peace and save lives. Gotta lock in those $trillions. Life be damned! Imbeciles!”

Elon Musk, a close Trump ally, claimed on his social media platform, X, that Russia would “respond reciprocally” to the US approval.

Some Russian officials openly voiced hopes that the incoming Trump administration would overturn the decision after taking office in late January. “These guys, Biden’s administration, are trying to escalate the situation to the maximum while they still have power and are still in office,” the Russian lawmaker Maria Butina said.

Starmer’s spokesperson said that the UK prime minister “wants allies to step up and support Ukraine” and that he intended to reflect that in his conversations with other leaders at the G20 in Rio de Janiero. The prime minister is not expected to have a one-on-one meeting with Biden, though they will see each other on the sidelines of the summit.

Similar language about Storm Shadow was also used by John Healey, the defence secretary, in the Commons on Monday. Giving the clearest hint yet that a positive decision on allowing Ukraine to use Storm Shadow inside Russia was expected, he told MPs: “I will not compromise operational security and comment on long-range systems today,” before adding that the UK recognised Ukraine needs extra help. “The prime minister has made clear, as I do to the House today, that we must double down on the support for Ukraine,” he said.