Two lions, who were in an animal shelter in Kyiv, are seen in an enclosure at "Natuurhulpcentrum" nature centre. [Natuurhulpcentrum VZW/Handout via REUTERS]

A Belgian animal shelter has taken in two young lions evacuated from Ukraine, who it says Russian troops had threatened to shoot when they encountered them outside Kyiv.

Twin males Tsar and Jamil, born in January 2021, were due to be transferred to Belgium in May after the Ukrainian authorities seized them from private owners who had mistreated them.

However, Russia's invasion of Ukraine meant the transfer had to happen immediately, with shelling of Kyiv, where they were held, causing them stress and injury as they jumped against their cages.

Frederik Thoelen, a biologist who has worked at the Belgian shelter since 2007, recounted the lions' tough five-day journey from Kyiv on Feb. 26 to Poland's Poznan zoo, beginning with an encounter with Russian military outside the Ukrainian capital.

"The Russian army, they pointed their guns at the carers. They threatened to kill the animals. The carers said 'no those are our animals. If you touch the animals you first have to touch us'," Thoelen told Reuters on Wednesday.

"So they risked literally their lives to save the animals. Eventually the Russian army let them through. Then they had a long, long way to the Polish border. They had to drive through different small routes to avoid the traffic jams," he continued.

The lions arrived at the Natuurhulpcentrum shelter, one of few able to provide immediate care to wild animals, late on Tuesday. The shelter will hold them in quarantine for three months and nurse them back to health before starting to look for permanent homes, such as sanctuaries in Africa.

The shelter said the lion twins were abnormally small when rescued, lacking essential elements such as calcium and malnourished after being fed expired meat, while X-rays revealed bone fractures.