OPCW says it's monitoring the situation closely in Ukraine

FILE PHOTO: Exterior view of the Organisation for the Prohibition of Chemical Weapons (OPCW) headquarters in The Hague

THE HAGUE (Reuters) -The Organisation for the Prohibition of Chemical Weapons (OPCW) is concerned by the recent unconfirmed report of chemical weapons use in Ukraine's port city of Mariupol, an OPCW spokesperson said on Tuesday.

"The (...) OPCW is monitoring closely the situation in Ukraine," the spokesperson added.

Earlier in the day, a senior U.S. defense official said the United States could not confirm the use of chemical agents in Mariupol, under siege by the Russian army.

The OPCW global chemical weapons watchdog also said it had "uninterruptedly been monitoring the situation around declared chemical industrial sites" in Ukraine, which has been under attack by Russia since end February.

Russia's defence ministry has not responded to a Reuters request for comment. Russian-backed separatist forces in the east denied using chemical weapons in Mariupol, the Interfax news agency reported.

Chemical weapons production, use and stockpiling is banned under the 1997 Chemical Weapons Convention.

The mayor of Mariupol said the latest estimate was that about 21,000 civilian residents of the port city had been killed since the start of Russia's invasion.

(Reporting by Anthony Deutsch; Writing by Benoit Van Overstraeten; Editing by Chizu Nomiyama)