Kuwait withdrew one of its diplomats from New Zealand following an allegation of assault.
The envoy was removed after the Middle Eastern country declined to waive diplomatic immunity.
The police said they were called to a central Wellington address in the early morning of November 18, 2015.
"This involved an allegation of assault by a diplomat from the Embassy of the State of Kuwait."
But the police investigation halted when a request on their behalf last year by the Ministry of Foreign Affairs and Trade (Mfat) for Kuwait to waive diplomatic immunity was rejected.
As a result, the Ministry asked Kuwait to withdraw the diplomat.
The Ministry would not name the diplomat.
"The process of diplomatic immunity is set out in long-established international law under the Vienna Convention on Consular Relations 1963," the Ministry said.
"New Zealand is explicitly clear with diplomatic missions that we expect them to act in accordance with New Zealand laws, and that we will request immunity be waived if allegations of a serious crime are made."
Last year, Malaysian diplomat Muhammad Rizalman bin Ismail was sentenced to nine months' home detention after he broke into the home of a Wellington woman without his pants and defecated outside her home.
He had left New Zealand in 2014 despite facing attempted rape charges after a botched email gave Malaysian officials the impression he was entitled to diplomatic protection and it would be acceptable for Rizalman to return to Malaysia.
He was returned under extradition in October 2015 and later pleaded guilty to indecent assault.
The Herald reported last year that more than 60 diplomatic staff or family members had sought immunity for offences committed in New Zealand in the preceding 20 years, including for 25 serious criminal matters of a sexual or violent nature.
New Zealand officials applied to have diplomatic immunity waived in 13 of these cases, which range from drink-driving to assault, and a waiver was granted on seven occasions.
The ministry told the Herald last year New Zealand had lifted diplomatic immunity for its overseas envoys twice in 10 years.