New Zealand and the Cook Islands signed a Defense and Security Declaration in Rarotonga on Thursday, Wellington said in a statement.
The declaration came after the self-governing South Pacific Island nation signed a pact with China last year, which had triggered tensions with New Zealand.
New Zealand Foreign Minister Winston Peters said in a statement that the strategic environment that the two sides face "is more complex and contested today than at any other point since New Zealand and the Cook Islands formed our free association relationship in 1965."
"In that context, it's vital that New Zealand and the Cook Islands are clear, with one another and third parties, about the nature of our special relationship and our responsibilities to one another in the defense and security domains," he added.
Peters acknowledged that the two governments have had "a series of serious disagreements since late 2024."
"This Declaration resolves… ambiguity and provides clarity to both Governments so that we can move forward focused on the future, not the past," he added.
Tensions had erupted after New Zealand asked the Cook Islands to share details of its pact with China, whose details remain scant.
The Cook Islands, home to a little over 15,000 people, maintains free association, sharing a head of state and citizenship rights.
Addressing reporters in Beijing, China's Foreign Ministry spokeswoman Mao Ning said the Cook Islands is an "important cooperation partner in the South Pacific," and the two sides treat each other as "equals."
Beijing's ties with the island nation do "not target" third countries, and "should not be disrupted" by any third party, Mao said.
