New Zealand has turned down a United Nations request to provide a warship for piracy patrols, probably off the coast of Africa.

Defence Minister Wayne Mapp said the navy had too much on currently to send one of its two Anzac frigates.

"We have decided to defer any contribution until next year," Dr Mapp said.

"At the moment there are too many commitments in our own country and in the region."

Earlier this year Dr Mapp's office confirmed the Government was considering a request from the United Nations to send a warship.

New Zealand has been asked several times in the past by the United Nations to supply a warship for piracy patrols but said it did not have a craft available.

Piracy was estimated to cost $21 billion around the world each year, particularly in the waters between the Red Sea and Indian Ocean, off the Somali coast, and also in the Strait of Malacca between Indonesia, Malaysia and Singapore.

A surge in piracy off the Somali coast has led to an international bid to patrol the waters near the Horn of Africa.

Modern pirates often used small boats and carry small arms such as AK47 assault rifles and rocket propelled grenades to stop large cargo ships, including oil tankers, and hold them for ransom.