WASHINGTON, (Reuters) – The United States can’t confirm that chemical agents were used in Ukraine’s port of Mariupol. This was stated by a top U.S. defense officer on Tuesday.

Hanna Malyar (Deputy Defense Minister of Ukraine) stated that Russia might have used chemical weaponry while occupying Mariupol.

According to the U.S. official speaking under anonymity, “We can’t confirm the use chemical agents at this point.”

An official stated that the United States didn’t have information supporting the Russian movement of chemical agent near Ukraine.

U.S. President Joe Biden said last month that Russia’s unsubstantiated allegations against Kyiv of chemical and biological weapons suggest that Russian President Vladimir Putin is considering using those weapons in Ukraine.

Chemical weapons use, production and stockpiling are all prohibited under the Chemical Weapons Convention 1997. White phosphorous, although it is condemned by human right groups, isn’t banned under this convention.

Russia’s defense ministry didn’t immediately reply to Reuters’s request for comment. The Interfax news agency reports that Russian-backed separatist forces from the east deny using chemical weapons in Mariupol.

The Russians gave up on their attempt to seize the capital Kyiv after their forces were overwhelmed by resistance from Ukraine. They are now doubling their efforts east, where a U.S. official stated that a Russian convoy was about 60 km (37 miles) away from Izyum.