New Zealand Prime Minister Jacinda Ardern has used a foreign policy speech in Australia to call for reform to the United Nations following Russia’s invasion of Ukraine.

Speaking at the Lowy Institute in Sydney, Ms Ardern said the global body needed to be improved so Russia could be further held to account for its military action.

“We must reform the United Nations so that we don’t have to rely on individual countries imposing their own autonomous sanctions,” she said on Thursday.

“We must also resource the International Criminal Court to undertake full investigations and prosecution of the war crimes and crimes against humanity committed in Ukraine.”

New Zealand is set to be a third party in Ukraine’s case against Russia in the International Court of Justice following the invasion earlier this year.

Ms Ardern identified the UN’s failure to act on the conflict due to Russia’s position in the body’s Security Council, describing it as a morally bankrupt position.

“Under these circumstances, waiting for our multilateral institutions to act was not an option for New Zealand,” she said.

The prime minister said diplomacy needed to be the strongest tool to de-escalate tensions in the region, saying the conflict shouldn’t be characterised as a war of the West against Russia.

“We won’t succeed, however, if those parties we seek to engage with are increasingly isolated and the region we inhabit becomes increasingly divided and polarised,” she said.

“We must not allow the risk of a self-fulfilling prophecy to become an inevitable outcome for our region.”

Ms Ardern is on an Australian visit aimed at strengthening trade and security ties.

Her comments came as Russia’s ambassador to Australia said the relationship between the two countries had reached their lowest point in decades due to the federal government’s support of Ukraine.

The Australian government’s decision to impose sanctions on Russia and Russian nationals and provide lethal and non-lethal military aid to Ukraine was “very sad”, Russian ambassador Aleksey Pavlovsky said.

“I wish I could say something positive about Russian-Australian relations but they have reached probably the lowest point in decades,” he told ABC radio on Thursday.

“Whatever co-operation we had has been destroyed by the Australian side without really giving much thought to what Australia’s interests were.

“(It is) just for the sake of moving in lockstep with its allies and this is really sad.”

Prime Minister Anthony Albanese visited the Ukraine’s capital Kyiv this week to express Australia’s solidarity with the war-torn country.

Foreign Minister Penny Wong will soon come face-to-face with Russian counterpart Sergei Lavrov for the first time since the invasion in February.

Senator Wong is attending a G20 foreign ministers’ meeting in Bali this week and the talks are expected to be overshadowed by the war in Ukraine and Mr Lavrov’s presence.

The Group of 20 includes Western countries that have accused Moscow of war crimes in Ukraine and rolled out sanctions, and nations such as China, Indonesia, India and South Africa that have not followed suit.

Australia is the largest non-NATO contributor to Ukraine’s battle to oust the invading Russian army and has provided $390 million in military and humanitarian assistance.

It has also sanctioned 843 individuals and 62 Russian entities.

– AAP