The Prime Minister wants to see the people accused of shooting down Malaysia Airlines flight MH17 a year ago held to account.
Australian Foreign Minister Julie Bishop is in New York to push for a tribunal to investigate.
The tribunal would be set up by the UN Security Council and its current chair, New Zealand.
John Key says they're debating the best way to achieve accountability.
"It's not a question of whether there should be accountability, there should be. But how do we make sure that can ultimately pass the support of the other security members?" Mr Key said at his post-Cabinet press conference yesterday.
A debate needs to happen around the best framework for a tribunal to work under, he said.
"It's important that whatever the Security Council decides to progress and us as the chair decide to progress that it can go all the way – in other words, if it was decided it would be a tribunal that tribunal could actually be established and under what terms."
New Zealand's month-long presidency of the Security Council ends this week.
MH17 was shot down over eastern Ukraine in July last year, killing 298 people.