Labour leader Sir Keir Starmer has been warned he could ignite a civil war in his party if he follows through with threats to expel Nato-sceptic MPs.

He told Times Radio on Tuesday he will be “very clear and firm” with MPs questioning the party’s “unshakeable support” for the military alliance.

“We’ve been very clear about the expectations of our Members of Parliament when it comes to issues like antisemitism, when it comes to the false equivalence that some argue between Russian aggression and the acts of Nato,” he said.

Asked if he would act against his MPs, he answered: “Yes, these are principles that are absolutely the root of the Labour Party.”

Responding to Sir Keir’s comments, left-wing campaign group Momentum vowed to fight against any such moves.

Mish Rahman, a senior Momentum figure on Labour’s National Executive Committee, said: “Keir ran on a platform to end factionalism, unite the Labour Party and defeat the Tories. But after months of attacks on the Left, this anti-democratic move would spell the end of the Labour Party as we know it.

“A broad church which has held together for over a century would be torn down, wrecking Labour’s prospects with young people and minority communities represented by a new generation of left-wing Labour MPs of colour.

“There is absolutely no mandate within Labour for such divisive, authoritarian action in the party, and we would fight it all the way.”

It comes after The Times earlier reported that Sir Keir’s allies are urging him to purge “hard-left” MPs from the party before the next general election in a bid to further distance himself from his predecessor Jeremy Corbyn.

In their sights are understood to be 11 Labour MPs – including left-wingers Diane Abbott and John McDonnell – who signed a Stop The War Coalition statement critical of Nato at the start of Russia’s invasion of Ukraine.

The statement said Nato “should call a halt to its eastward expansion”.

After being threatened with the removal of the whip, all the names were withdrawn, with a party spokesperson saying the move showed Labour was “under new management” with Sir Keir.