President Joe Biden’s apparent green light for Ukraine to strike Russia with US-made long-range missiles has caused consternation among some of Donald Trump’s allies.

Trump himself has not commented, but he won the election after promising to end the war – and several people close to him have condemned the move as dangerous escalation.

Biden has committed tens of billions of dollars to Kyiv’s war effort, and at the weekend he reportedly ditched a long-standing red line on Ukraine’s use of American weaponry to launch attacks deep into Russia.

Donald Trump Jr tweeted that the president was trying to “get World War Three going” before his father took office.

Biden’s decision has not been formally confirmed and it may never be.

When asked about how typical it would be for a presidential administration to take such a significant policy decision in its final months, State Department spokesman Matthew Miller said that Biden was “elected to a four year-term, not a term of three years and 10 months.”

“We will use every day of our term to pursue policy interests that we believe are in the interests of the American people,” he said. “If the incoming administration wants to take a different view, that is, of course, their right to do so.”

“There’s one president at a time,” he added. “When the next president takes office, he can make his own decisions.”

Ukraine’s President Volodymyr Zelensky said no such announcement was forthcoming – “missiles will speak for themselves”.

Trump swept to victory on 5 November and is due to be back in the White House for a second term from 20 January next year.

Trump has campaigned on a promise to end the US involvement in wars and instead use taxpayers’ money to improve Americans’ lives.

He has said he will bring the Russia-Ukraine war to an end within 24 hours, without saying how.

One thing is certain, though: Trump has always seen himself as a dealmaker and will not want Biden to take any such credit.

His son, Donald Trump Jr, was among the first Republicans to respond.

“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,” he said.

Another vocal Trump supporter, Congresswoman Marjorie Taylor Greene, condemned Biden, too.

“The American people gave a mandate on Nov 5th against these exact America last decisions and do NOT want to fund or fight foreign wars. We want to fix our own problems,” she wrote on X.

Not all of Trump’s allies, including some who advised him on national security affairs during his first term, shared this view – though they were critical of the Biden administration’s approach.

James Gilmore, who served as Trump’s ambassador to the Organization for Security and Cooperation in Europe, told the BBC that the main issue with Biden’s decision to provide Ukraine this new capability is that it came so late in the war.

“My criticism of Biden is the same as every other conservative and supporter of Trump – which is that the Biden administration slow walked this,” he said.

Gilmore said he did not know what the president-elect would choose to do regarding Ukraine once he entered office. “I don’t believe that he’s a man that usually walks away,” he said.

Polls suggest a large number of Republicans want US support for Ukraine to stop – 62% told a poll by Pew Research the US had no responsibility to support the country against Russia.

Senator JD Vance, who will be Trump’s vice-president, has regularly objected to providing arms to Ukraine. He argued that the US lacks the manufacturing capacity to continue providing weapons like the missile systems that Kyiv will use to strike within Russia.

Gilmore, however, said the US was able to backfill and upgrade its weapon systems through this process, but he said the US’s European allies would need to take on a bigger role.

“President Trump is exactly right about this – the alliance is stronger when Western European countries step up to the plate,” he said. “The United States cannot continue to act alone. The taxpayer won’t permit it, the next administration won’t permit it, and I wouldn’t, either.”

Since launching the full-scale invasion of Ukraine in February 2022, Russia’s president has been railing against the US-led Nato alliance – and described every pledge of military support by the Western allies for Ukraine as a direct involvement and warned of retribution.

His spokesman said on Monday that the US was “adding fuel to the fire”.

At times, Putin has mooted the possibility of using nuclear weapons, too.

Few believe this may come to pass as, under the mutual-destruction doctrine established during the Cold War when nuclear arsenals were built up, Putin knows their use would bring untold suffering to all, including Russians.

But the Russian leader will be fully aware of the magnitude of the threat of Western-supplied long-range missiles.

The Institute for the Study of War, a think tank, has published a map of 225 Russian military installations within range of ATACMS.

Former US envoy to Ukraine, Kurt Volker, said Biden’s decision would enable Ukraine “to go after airfields, the ammunition depots and the fuels supplies, logistics that Russia has, which right now are in a sanctuary zone in Russia”.

Biden’s decision will cause Russia to be more cautious, Volker told the BBC.

Dismissing Putin’s threats, he said the Russian leader “should have anticipated that there would be efforts by Ukraine to fire back”.

Ukraine has had ATACMS as well as UK and French Storm Shadow missiles of similar range for some time, though the numbers are not known. But it has not been allowed to use them inside Russia.

France and the UK are expected to follow the US lead and issue the same authorisation to Ukraine. So far, they have not commented.

White House officials are emphasising to US media that Biden’s change of heart is in response to Russia’s deployment of North Korean troops – a signal to Pyongyang not to send any more.

Gilmore, Trump’s OSCE ambassador, told the BBC that he believes it is “Putin who has escalated the war” by deploying North Korean soldiers, and the US cannot “just stand aside and let this dictator go ahead and conquer Ukraine”.

“I don’t like it and I take it all very seriously, but the decision is not ours. The decision is being forced upon us by Putin – by the dictator,” he said.

The move also follows a barrage of Russian attacks on Ukraine in recent days.

One strike on Odesa on Monday killed 10 people, including seven policemen, and injured 47 others.