Australian officials are seeking to verify reports of the use of chemical weapons by Russia in Ukraine.
Ukraine President Volodymyr Zelenskyy warned of the potential Russian use of chemical weapons in a video address, with media reports suggesting they had been used in the battle for the port city of Mariupol.
Foreign Minister Marise Payne says the reports are "extremely concerning".
"If they are confirmed that will be a further wholesale breach of international law," Senator Payne told reporters in Sydney on Tuesday.
"(It's) a further indication of President Putin and Russia's absolute violation of every single value and every aspect of the rules-based global order which has stood us in such good stead for so many decades now."
Australian officials were working with counterparts to determine the veracity of the reports.
Pentagon press secretary John Kirby said on Monday the United States was aware of the reports.
"We cannot confirm at this time and will continue to monitor the situation closely," Mr Kirby said.
"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."
in retaliation to the Morrison government's sanctions on Russian elites.
"The sanctions are a badge of honour for Australia standing up for freedom," Prime Minister Scott Morrison said.
Senator Payne said the sanctions would not deter Australia from imposing "the maximum possible costs" on Russia over its unlawful invasion.
Overnight, Britain also confirmed it is trying to verify reports that Russia has used chemical weapons in an attack on Mariupol, London's top diplomat said.
"Reports that Russian forces may have used chemical agents in an attack on the people of Mariupol. We are working urgently with partners to verify details," Foreign Secretary Liz Truss wrote on Twitter.
"Any use of such weapons would be a callous escalation in this conflict and we will hold Putin and his regime to account."
Ukrainian politician Ivanna Klympush said Russia had used an "unknown substance" in Mariupol and that people were suffering from respiratory failure. "Most likely chem.weapons!" she tweeted.
Ukraine's Azov battalion in a Telegram message earlier on Monday had claimed a Russian drone dropped a "poisonous substance" on Ukrainian troops and civilians in Mariupol.
The force also claimed that people were experiencing respiratory failure and neurological problems.
The battalion's founder, Andrei Biletsky, said that three people were suffering effects from an unknown toxic substance.
"Three people have clear signs of poisoning by warfare chemicals, but without catastrophic consequences," he said in a video address on Telegram.
AFP was unable to verify the claims.
Senior Donetsk separatist official Eduard Basurin had spoken of the possibility of using chemical weapons against the southern port city that has resisted Russian bombardment for weeks.
Mr Basurin said the besieging forces could "turn to chemical troops who will find a way to smoke the moles out of their holes", Russian news agency RIA Novosti quoted him as saying on Monday.
Russia has denied committing any war crimes during its offensive in Ukraine.
