Stepping up the heated war of words over Ukraine, Russia on Tuesday accused US private military companies (PMC) of preparing provocations with the use of chemical weapons in eastern Ukraine.

Sergey Shoygu said some 120 US mercenaries are now working in Ukraine’s war-torn Donbas region, training the Ukrainian military "for active combat operations."

"It has been reliably established that there are more than 120 employees of American private military companies in the settlements of Avdiivka and Priazovskoye in the Donetsk region,” he told a meeting of the Russian Defense Ministry board in Moscow.

“They equip firing positions in residential buildings and socially significant facilities, train Ukrainian special operations forces and radical armed groups for active combat operations.”

The private firms also delivered "tanks with unidentified chemical components" to the cities of Avdiivka and Krasny Estuary "to commit provocations," Shoygu claimed.

Fighting between Ukrainian government forces and pro-Russian rebels in Donbas has seen more than 13,000 people killed since 2014, according to the UN.​​​​​​​

The region is one of several sources of friction between Russia and Ukraine, including Russia’s annexation of Ukraine's Crimea region, which the US, Turkey, and the UN General Assembly view as illegal.

Donbas is in the spotlight as it lies along Ukraine’s border with Russia, where a military buildup has rattled Western nerves.

As Western European countries warn Russia not to take any military action against Ukraine, Russia has accused Ukraine and its allies of provocations and raising tensions./aa