Ukraine has promised to negotiate the exchange of captured Australian Oscar Jenkins as the two nations reiterate their co-operation against Russia’s invasion.

Ukrainian ambassador to Australia Vasyl Myroshnychenko said his government had added Jenkins to its list of prisoners of war after Russian officials confirmed the 32-year-old Melburnian was alive and in captivity.

“He had a contract with the Ukrainian Defence Forces so all the international law applies to him. So he will get on that list,” Myroshnychenko told ABC TV on Wednesday.

There have been grave concerns for Jenkins’ safety since a video of him being interrogated by Russian soldiers in eastern Ukraine was circulated online in December.

Russia has previously expressed its view that foreign fighters serving with Ukrainian forces are mercenaries and can be liable to prosecution.

But as a prisoner of war, Jenkins would be entitled to legal protections under the Geneva Convention.

“The Ukrainian government certainly will be negotiating his exchange,” Myroshnychenko said.

“I understand the Australian government may do something similar but this is not for me to comment. I will definitely only talk on behalf of my own government.

“We have exchanged previously lots of prisoners of war and we swap them for Russian prisoners of war.”

Prime Minister Anthony Albanese raised Jenkins’ welfare directly with Ukrainian President Volodymyr Zelensky for the first time in a phone call overnight, ahead of the three-year anniversary of Russia’s invasion of Ukraine.

Zelensky called for an investigation into how Jenkins ended up in Russian hands.

“We must establish all the circumstances surrounding the case of Australian citizen Oscar Jenkins, who fought for Ukraine and has been taken prisoner by Russia,” he wrote on X.

Zelensky thanked Mr Albanese for Australia’s “unwavering” support of Ukraine and said the two countries were working to expedite a new defence aid package.

“We discussed strengthening sanctions against Russia for its war, and Australia is ready to take further steps,” he said.

“We also addressed diplomatic efforts and appreciate Australia’s firm stance that all substantive negotiations on Ukraine must include Ukraine – this is the only way to achieve a just peace.”

It will be three years since Russia commenced its full-scale invasion of Ukraine on February 24.

-AAP