UK refuses to rule out 'direct Nato involvement' amid fears of chemical weapons attack in Ukraine

The UK has warned Vladimir Putin "all options are on the table" if Russia is found to have used chemical weapons in Ukraine.

Defence minister James Heappey also appeared to refuse to rule out "direct Nato involvement" in the conflict, a move that would represent a significant escalation in tensions between Russia and the West.

On Monday, Ukrainian officials said they were checking unverified reports that Russia had used chemical weapons - possibly phosphorous munitions - in the southern port city of Mariupol, causing soldiers and civilians to show signs of respiratory illnesses.

“Russian occupation forces used a poisonous substance of unknown origin against Ukrainian military and civilians in the city of Mariupol, which was dropped from an enemy [unmanned aerial vehicle],” the Azoz Regiment, a unit of the National Guard of Ukraine, said in a post on Telegram.

“The victims have respiratory failure, vestibulo-atactic syndrome.”

Speaking to BBC Radio 4’s Today programme, armed forces minister James Heappey said: “I think it’s important that everybody is clear that the reports overnight haven’t been verified.

Read more: Drone footage shows aftermath of Russian bombing in Mariupol as death toll 'hits 10,000'

“But if they were used, the Prime Minister, the president of the United States, the president of France and other world leaders have all been clear that that crosses a line and that all options are on the table to how we would respond.”

Pressed on whether “all options” would mean direct Nato involvement, Heappey said: “Well I think some ambiguity is useful but all options mean all options."

He added: "It’s also not for any government minister from an individual country to pledge Nato involvement.

“It’s perfectly possible that a response to chemical weapons use could happen outwith Nato but all options being on the table is meant as a very clear deterrent to President Putin from using these weapons that are utterly appalling, cause huge suffering and misery, are completely indiscriminate, and won’t just affect troops – not that that’s not bad enough – but could well affect women, children, civilians.”

In march, Nato secretary general Jens Stoltenberg said the use of chemical weapons would be a “blatant violation of international law with far-reaching consequences.”

Ukrainians reported the alleged chemical attack over social media.

“ATTENTION! Chemical weapons are used against Ukrainian defenders in #Mariupol! russia openly crosses all boundaries of humanity and openly declares it,” Anton Gerashchenko, an adviser to Ukraine’s minister of internal affairs, said on social media.

Watch: Drone footage shows devastation of Mariupol

The Pentagon confirmed it had not verified the claims, but said it was monitoring the situation closely.

“These reports, if true, are deeply concerning and reflective of concerns that we have had about Russia’s potential to use a variety of riot control agents, including tear gas mixed with chemical agents, in Ukraine,” press secretary John Kirby said in a statement.

Since launching an invasion of Ukraine on 24 February, Russia has been accused of carrying out a number of war crimes.

Ukraine accused Russian troops of killing hundreds of civilians in the town of Bucha, just outside of Kyiv, following their retreat.

On Thursday, Russia was expelled from the UN Human Rights Council after delegates voted 93 to 24 to remove them following allegations of Russian soldiers carrying out mass killings, rape and torture.

The vote came after a push from the US, with the draft text for the vote expressing "grave concern at the ongoing human rights and humanitarian crisis in Ukraine".

Fifty-eight nations abstained from the vote.

A two-thirds majority of voting members in the 193-member General Assembly in New York was needed to suspend Russia from the 47-member Geneva-based Human Rights Council.