Iran and Russia on Wednesday denounced the UK's decision to bolster its nuclear arsenal, with the Islamic republic accusing it of "hypocrisy" and the Kremlin warning the move threatens international stability.
Britain announced Tuesday that it plans to increase its nuclear arsenal from 180 warheads to 260 by the end of the decade, as it published a document outlining a recalibration of its foreign policy.
The move reverses a previous commitment by London to reduce its stockpile.
Britain had repeatedly criticised Iran for resuming parts of its civil nuclear programme, which it had given up under a 2015 deal later abandoned by former US president Donald Trump, but now broadly supported by his successor Joe Biden.
"In utter hypocrisy, (British Prime Minister) @BorisJohnson is 'concerned about Iran developing a viable nuclear weapon'," Iran's Foreign Minister Mohammad Javad Zarif tweeted.
"On the very same day he announces his country will increase its stockpile of nukes.
"Unlike the UK and allies, Iran believes nukes and all WMDs (weapons of mass destruction) are barbaric & must be eradicated."
- 'Credible deterrence' -
Britain's announcement also drew criticism from Russia, which was identified in the review as the "most acute direct threat to the UK".
"We are very sorry that the UK has chosen this path of increasing nuclear warheads. This decision harms international stability and strategic security," Kremlin spokesman Dmitry Peskov said.
"The presence of nuclear warheads is what threatens peace throughout the world."
Britain on Wednesday insisted its plan was the "minimum" required to maintain its deterrence capability.
Foreign Secretary Dominic Raab identified Russia and Iran, as well as North Korea, as states guilty of "predatory opportunism".
"We're making sure we can maintain, at minimum, a credible deterrence," Raab said.
"We want to see a nuclear-free world but... I don't think it's going to happen by unilaterally giving up the ultimate insurance policy that we need and, with respect, that the US needs."
France, also a nuclear power, said it "fully respects" Britain's decision, with the foreign ministry calling London a "strategic partner and ally".
Under the terms of the nuclear Non-Proliferation Treaty, which went into effect in 1970, Britain is one of a handful of recognised nuclear powers.
Fellow signatory Iran has no such recognition, and by signing the NPT committed itself never to acquire or manufacture a nuclear weapon.
Iran has consistently denied any such ambition, although its arch foe Israel, itself widely suspected of having an undeclared nuclear arsenal, has repeatedly accused Tehran of covertly seeking the bomb.
The 2015 nuclear deal with Iran, which Britain and other European governments are seeking to revive, was an attempt to assuage such concerns.
On Wednesday, a senior Israeli military official told AFP that army chief Aviv Kochavi was not opposed to a new deal -- as long as it makes it "practically impossible" for Tehran to acquire nuclear weapons.
- 'Toxic masculinity' -
The UK's move is at odds with a January deal between Moscow and Washington to extend a key bilateral nuclear pact, that was the last remaining arms reduction agreement between the Cold War rivals.
Moscow has also pushed for Washington and Tehran to return to the Iran nuclear deal.
Signed in 2015, the accord offered sanctions relief in exchange for curbs on Tehran's nuclear ambitions and guarantees it would not seek an atomic bomb.
However its signatories are scrambling to keep it alive after Trump unilaterally withdrew from it in 2018 and imposed sanctions on Iran.
Tehran then responded by progressively rolling back on its commitments under the deal, although it has insisted that all these moves are reversible.
Britain's foreign policy document also identified Russia as the "most acute direct threat to the UK," posing "the full spectrum" of dangers.
Peskov on Wednesday said the UK had cited "an ephemeral threat" without "an explanation".
"This is not true," he added. "No threat comes from Russia."
Ties between Moscow and London have greatly deteriorated in recent years, not least over poisonings of Russian defectors on UK soil.
Russia's broader relations with the West are at their lowest point since the Cold War, marred by allegations of election interference and sweeping cyberattacks.
Britain's announcement has also been condemned by the Campaign for Nuclear Disarmament (CND) and the International Campaign to Abolish Nuclear Weapons (ICAN).
ICAN's chief Beatrice Fihn called the move "toxic masculinity on display".