Russia's defence ministry accused Ukraine on Saturday of poisoning some of its servicemen in the Russian-controlled part of Ukraine's southeastern region of Zaporizhzhia in late July.
An adviser to Ukraine's interior ministry said in response that the alleged poisoning could have been caused by Russian forces eating expired canned meat.
The Russian defence ministry said a number of Russian servicemen had been taken to a military hospital with signs of serious poisoning on July 31. Tests showed a toxic substance, botulinum toxin type B, in their bodies, it said.
"On the fact of chemical terrorism sanctioned by the (Ukrainian President Volodymyr) Zelenskiy regime, Russia is preparing supporting evidence with the results of all the analyses," the ministry said in a statement.
It did not say how many servicemen had suffered or what their condition was now. It did not say what the "supporting evidence" was.
Botulinum toxin type B is a neurotoxin that can cause botulism when ingested in previously contaminated food products, but it can also have medical uses.
Ukraine's defence ministry did not immediately respond to a Reuters request for comment, but interior ministry adviser Anton Gerashchenko commented on the Russian allegation on the Telegram messaging app.
"The department (Russian defence ministry) does not clarify whether the poisoning could have been caused by expired canned meat, in which botulinum toxin is often found. Overdue rations have been massively complained about by the occupying forces since the first days of the invasion of Ukraine," he said.
The Russian defence ministry said it was conducting an additional investigation into an incident in which Volodymyr Saldo, the Russian-installed administration in Ukraine's occupied Kherson region, was taken ill.
Saldo, a former mayor of the city of Kherson who was appointed to head the region of the same name when Russian troops overran it in early March, fell ill in early August.
Russia says its "special military operation" launched on February 24 is aimed at demilitarising Ukraine and protecting Russian speakers on what President Vladimir Putin called historical Russian land.
Ukraine and Western countries view it as an unprovoked war of conquest aimed at wiping out Ukraine's national identity.