UPDATED 1.35pm: John Key has pushed for reform of the United Nations Security Council.

The Prime Minister has just delivered a speech to the UN General Assembly in New York.

LISTEN ABOVE: John Key's full speech at the UN General Assembly in New York.

He said it's time for the Security Council to step up, to stop talking about what's right - and do what's right.

In his speech to the United Nations General Assembly in New York, the Prime Minister said there must be a political solution to the conflict in Syria - and it must come soon.

"All Council members carry responsibility for ending the misery in Syria and beyond. The consequences of inaction are not theoretical, the human toll is real."

He believes the Security Council has failed to act over the past four years.

Mr Key said part of the problem is structural.

"The fact that the five permanent members of the council have the veto creates an extraordinary power imbalance. That imbalance is exacerbated by their practices of pre-negotiating outcomes before engaging with elected members."

John Key said New Zealand will be supporting a proposal put forward this year to limit the use of the veto in mass atrocity situations.