Pentagon monitoring reports of possible Russian chemical weapons attack in Mariupol

Armoured vehicles of pro-Russian troops drive along a street during Ukraine-Russia conflict in the besieged southern port city of Mariupol, Ukraine March 31, 2022. 

The Pentagon was keeping a close eye on reports of a possible Russian chemical weapons attack on the besieged Ukrainian city of Mariupol.

It would be a challenge to NATO to act if Russia were found to have used chemical weapons in the city.

Kirby said that they are aware of social media reports that claim Russian forces deployed a potential chemical munition in Mariupol.

Kirby said that the reports are concerning and reflective of concerns that we have had about Russia's potential to use a variety of riot control agents.

British Foreign Secretary Liz Truss said that her government was working to verify details of an alleged attack.

The original report was posted on Telegram by the Azov Regiment, an ultra-nationalist part of the Ukrainian National Guard. Russian forces used a poisonous substance, according to the Azov message.

Any use of such weapons would be a callous escalation of the conflict and we will hold Putin and his regime to account.

The US has warned for several days that the Russian army will almost certainly continue to commit atrocities in the eastern regions of Ukraine.

Kirby told reporters earlier in the day that Russian leaders have shown their brutality in the past.

This is breaking news. You can check back for updates.