The United States has been granted permission to sail a Coast Guard icebreaker into New Zealand waters this month.

The Polar Star's stop-off in Christchurch will be the second visit by a US ship since anti-nuclear legislation was passed in 1987, following a visit by the USS Sampson in November.

The 122m long, diesel-powered icebreaker will dock at Lyttelton after completing operations at the US scientific base in Antarctica, where it breaks a channel through the ice for a cargo ship and fuel tanker. Those ships also provide supplies for New Zealand's Scott Base.

US Charge d'Affaires Candy Green said stopping in New Zealand made sense because it saved days of transit and freed the C-130 Hercules cargo planes to carry out missions on the ice.

The possibility of further visits would be decided on a case-by-case basis between the two countries, she said.

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"Any conversations about the possibility of future visits will focus on practical cooperation, friendship, and advancing shared interests."

The USS Sampson's attendance at the Royal New Zealand Navy's 75th anniversary in November ended a 33-year gap in visits by US vessels to New Zealand. While in the country, it also helped evacuate people after the Kaikoura earthquake.

New Zealand's anti-nuclear law forbids any vessel carrying nuclear arms or which is nuclear powered from entering New Zealand waters. The Prime Minister needs to approve any visit.

The US has a long-standing policy of refusing to confirm or deny whether its ships have nuclear capabilities. However, New Zealand officials can often find out if they are nuclear capable from publicly available information about ships' specifications.