"Ukraine has never asked us," the NZ prime minister said.

Like Australia, NZ is considering its next moves to support Ukraine in the conflict, set to enter a damaging new phase.

In an address from Moscow on Wednesday, Russia president Vladimir Putin said he would call up hundreds of thousands of reservists to fight.

Later, Ukraine President Volodymyr Zelenskiy spoke to the UN General Assembly via video, calling for more support and a war tribunal to punish Russia for its actions.

Speaking at sidelines of the UN gathering, Australian foreign minister Penny Wong said expelling the Russian ambassador "remains under consideration".

Ms Ardern echoed Ms Wong's line, saying her government has kept that option live from the start of the invasion in February.

However, the Kiwi leader said she is more focused on providing material support to aid Ukraine's resistance, while blunting Russia's coercion.

"We've always had a range of options on the table. Expelling the Russian ambassador has always been one of those options," she told journalists in New York.

"Of all the things we could do, it is one of the least meaningful in this situation.

"Having met just yesterday with the prime minister of Ukraine, I really am firming up the view the most important thing we can be doing, first and foremost, (is) sanctions and also supporting them as we have in the ongoing fight within Ukraine.

"We've always said we want dialogue and diplomacy to end this war. You lessen your opportunities when you don't have those representatives."

Ms Ardern said NZ had heeded Ukraine's call to punish Mr Putin's regime for its "illegal and immoral" war, and would want to help shape compensatory and restitution efforts.

"Our view is there must be accountability. The question is only in what form that takes," she said.

"We want to be part of all those conversations."

While Mr Putin's latest address has pushed Russia's invasion to the forefront of many minds, Ms Ardern said it had not dominated her agenda in New York.

Overnight, she held meetings with UN Secretary General Antonio Guterres and Chile President Gabriel Boric.

According to reports, she will cap her day by co-hosting a meeting with Fiji Prime Minister Frank Bainimarama for Pacific leaders.

"The majority of my day-to-day has has been spent talking with other leaders about the crisis of climate change and the impact on small island nations," Ms Ardern said.

"We have multiple crises we are dealing with as an international community."

Australian Associated Press