"We, like most of our like-minded partners, have not exercised that option because that is one of the least meaningful in this situation."
Expelling Russia's ambassador to New Zealand would likely lead to the expulsion of New Zealand's ambassador to Russia, meaning any New Zealanders in Russia could struggle to get help. It would also cut off a channel for diplomacy.
Ardern said that "sanctions send the strongest message" and pushed back on the idea that Russia was not feeling the diplomatic reprisals of the invasion.
"Sanctions send the strongest message. We as politicians have all been banned from travelling to Russia for our sanctions, not because of diplomatic expulsions."
The remarks were in response to comments from Foreign Minister Nanaia Mahuta that were interpreted as New Zealand inching towards expelling the ambassador.
Ukraine continues to dominate high-level week at the United Nations in New York, where leaders from more than 150 countries have gathered.
At a meeting of the powerful Security Council on Friday morning, New Zealand time, the United States secretary of state Antony Blinken came face-to-face with his Russian counterpart, Foreign Minister Sergey Lavrov.
Lavrov called Ukrainian President Volodymyr Zelenskyy, a "bastard", and appeared to slight the council by arriving 90 minutes late to the meeting and leaving early.
Blinken slammed Putin for his veiled nuclear threat and called on him to end the war.
"Every council member should send a clear message that these reckless nuclear threats must stop immediately," Blinken said.
"Tell President Putin to stop the horror he started."
Ardern had her most high-profile meetings of her trip to the United Nations so far overnight, New Zealand time.
She met with UN Secretary-General António Guterres at the United Nations, and attended a reception with US President Joe Biden at the Natural History Museum.
Ardern said their conversation was also related to Ukraine, and the perspective of "our part of the region on that conflict".
She said they discussed generally how to "continue to make sure that we have that international community in its full force across regions, not just in Europe but of course across Asia, the Pacific, Latin America, the Caribbean, that it is very clear that the international community stands united on this clear breach of the international rules and order".
Ardern said she had "a very brief" exchange with Biden at his reception.
She said it acknowledged the "relationship that New Zealand and the United States have".
