Ardern told Newstalk ZB broadcaster that the Russian diplomats, which will be expelled from these countries, were undeclared intelligence officers.
"We ran a check, we don't have those in New Zealand but if we did we would expel them," Ardern said as quoted by the broadcaster.
US President Donald Trump, in particular, ordered the expulsion of 60 Russian diplomats, including 48 employees of the Russian Embassy and 12 people who have been assigned to the United Nations in New York, as well as the closure of the Russian Consulate in Seattle.
Skripal, a former GRU colonel and a double agent who worked for UK intelligence, and his daughter Yulia have been in hospital in a critical condition since March 4 due to exposure to what the UK experts say was a A234 nerve agent. UK Prime Minister Theresa May has accused Russia of orchestrating the attack and expelled 23 Russian diplomats, while the European Union has expressed its solidarity.
The Russian side has strongly rejected the accusations and offered assistance in the investigation. Moscow's request for samples of the chemical substance used to poison Skripal was rejected. Moscow expelled UK diplomats in response and ordered the British Council to cease its activities in Russia.