Ukrainian officials have denounced a call on social media by Russia’s embassy in Britain for members of the Azov Regiment to face a “humiliating death."

The Russian post on Twitter came hours after an attack on a prison complex in an area of the Donetsk region in eastern Ukraine that is under Russia-backed separatist control.

Dozens of Ukrainian prisoners of war were apparently killed in the incident, reportedly including members of the Azov Regiment.

Russia claimed Ukraine’s military used U.S.-supplied precision rocket launchers to target the prison in Olenivka.

The Ukrainian military, however, denied making any rocket or artillery strikes in Olenivka. It accused the Russians of shelling the prison to cover up the alleged torture and execution of Ukrainians there.

In its tweet, the Russian Embassy in Britain said: “Azov militants deserve execution, but death not by firing squad but by hanging, because they’re not real soldiers. They deserve a humiliating death.”

Twitter said the embassy had violated its rules on “hateful conduct” but put a warning on the tweet rather than banning the post about the Azov Regiment, a Ukrainian battalion that retains some far-right affiliations.

Andriy Yermak, the head of the presidential office, said Russia was a “terrorist state.”

“In the 21st century, only savages and terrorists can talk at the diplomatic level about the fact that people deserve to be executed by hanging. Russia is a state sponsor of terrorism. What more evidence is needed?” Yermak wrote on Telegram.

Ukrainian Foreign Ministry spokesman Oleh Nikolenko tweeted that "there is no difference between Russian diplomats calling for execution of Ukrainian prisoners of war and Russian troops doing it in Olenivka. They are all accomplices in these war crimes and must be held accountable."

Ukrainian forces, including members of the Azov Regiment, ended a weeks-long siege of the vast Azovstal plant in Mariupol by agreeing to surrender in May.

Around 2,500 combatants were taken captive by Moscow's forces after calling a halt to their resistance.

The Azov regiment is a former volunteer battalion that has drawn controversy for its links to far-right figures.

The group was formally incorporated into Ukraine's National Guard in 2014 when its members fought alongside Ukrainian forces against Russia-backed separatists in the eastern Ukraine’s Luhansk and Donetsk regions.

With reporting by AFP