Ukraine president urges world not to give in to Russia’s ‘nuclear blackmail’ during Australian address

Ukraine's president, Volodymyr Zelenskiy, has urged world leaders not to give in to Russia's "nuclear blackmail" and has appealed to Australia for help in a critical UN vote next week.

Addressing the Sydney-based Lowy Institute by video link on Thursday evening, Zelenskiy revealed Australia was offering heavy arms to Ukraine in its next package of military support to defend against Russia's invasion.

The UN general assembly will consider a resolution condemning Russia's purported annexation of four partly occupied Ukrainian regions, but Russian officials are lobbying for a secret vote so countries don't have to make their positions public.

Zelenskiy asked Australian officials to join in diplomatic efforts to ensure next week's UN vote was "as unanimous as possible".

"I'm asking Australia to use all of its influence to convince as many countries as possible not to remain neutral and to vote for international law and against a Russian annexation," he said during the Lowy Institute event.

Zelenskiy called on as many countries as possible to join in the "clear and straightforward condemnation" of the Kremlin, saying the Russian president, Vladimir Putin, would escalate further if the response was "weak".

Putin has threatened to use all means at his disposal to defend Russian territory and has said the four Ukrainian regions would be part of Russia "forever".

Zelenskiy said on Thursday: "So even if he would decide to launch a nuclear strike, well, what can I say? I think the world will never forgive this.

"I think he clearly understand that after the use of [nuclear] weapons, he would be unable any more to preserve - so to say - his life and I'm confident of that."

Zelenskiy thanked Australia for its "very meaningful defence" assistance, saying the Bushmaster protected mobility vehicles had "performed masterfully".

"There's also a significant package that Australia has been preparing," he added.

"This process is ongoing as we speak and I'm very grateful for that. I don't want to go into details on what weapons, what's inside this package, but it's not only small arms but some heavy weapons as well."

He urged Australia to continue to ratchet up sanctions against Russia, because the pressure campaign would be most effective if "the aggressor does not have time to circumvent those sanctions".

Zelenskiy said Ukraine's recapture of territory that Russia had claimed showed the Kremlin was not capable of holding its ground. "They can kill but they cannot survive," he said.

Asked about Ukraine's bid to join Nato, announced last week, Zelenskiy said the alliance had to "demonstrate that they are not afraid of Russia". But the timeline for joining Nato was unclear, and "unfortunately depends not only on Ukraine", he said.

Ukraine's forces have been trying to advance in the east and south of the country, prompting a rare admission from Putin that his troops were under pressure.

Putin said earlier this week that Russia would "stabilise" the situation in the four Ukrainian regions - Donetsk, Luhansk, Kherson and Zaporizhzhia - it claimed as its own territory last week. Australia and other countries have refused to recognised the purported annexations.

Australia has gradually ramped up its assistance to Ukraine since February, first under the Morrison government and now under the Albanese government, and ministers are now considering further expanding that help amid expectations of a "protracted" conflict.

Australia's $388m in pledged military assistance to Ukraine includes 60 Bushmaster vehicles, unmanned aerial systems, anti-armour weapons and equipment to remove bombs littering the battlefield.

Both major parties in Australia have said helping Ukraine respond to Russia's "illegal, immoral" invasion is important for broader preservation of international stability - including in the Indo-Pacific, where China has not ruled out taking Taiwan by force.

The defence minister, Richard Marles, said the Australian government was considering longer term support "to put Ukraine in a position where ultimately this conflict can be resolved on its terms".

"The unprovoked aggression from Russia in respect of Ukraine, is such a flouting of the UN charter, of the global rules-based order, it must not be allowed to stand," Marles said after a meeting with his American and Japanese counterparts in Hawaii last weekend.

So far, however, Australia has stopped short of expelling Russian diplomats - a move officials fear would trigger retaliatory expulsions of Australian diplomats in Moscow.

Zelenskiy made a direct appeal for Bushmaster vehicles when he addressed the Australian parliament by video link in late March - equipment that Canberra later agreed to supply.

Earlier this week, Ukraine's defence ministry posted video of its forces using an Australian-supplied Bushmaster to tow a Russian amphibious armoured personnel carrier.