Prime Minister John Key says a ceasefire in Syria will make the Security Council meeting he is chairing next week even more important for finding longer term resolution to halt the bloodshed.

A ceasefire in Syria was brokered between the US and Russia to allow humanitarian aid to get into areas such as Aleppo, where attacks have long prevented help getting to citizens.

Key said the ceasefire was an encouraging development as he heads to New York for leaders' week at the UN.

Key will take a turn in the chair leading a discussion on Syria at the Security Council. New Zealand is president of the powerful council for this month and chose Syria as the focus for the week the country's leaders would be in New York.


Key said that would be one of New Zealand's "biggest moments" on the Security Council.

"It's a time where New Zealand can use the Presidency ... to direct the world's leaders on the most pressing issue we face. If you think about what's been happening in Europe with the refugee crisis, all of those roads lead back to the Syrian crisis.

"Funnily enough the meeting we're holding is more important now because of the ceasefire, not less important. The ceasefire is just the point at which it gets people around the table. The real issue here is can you get the ceasefire to hold, who will sign up and what happens next?"

Key said that meeting could be "critically important" because the leaders of the US and Russia would both be in New York.

It was not yet known if US President Barack Obama would take part in the Security Council discussion in person, but he expected the US to be represented at a "logical level" given their role.

Key said hosting the meeting would also be a personal highlight.

"Sometimes you get really unique opportunities in this role - it's a privilege to be there. One of those is definitely going to be this. I think it will be one of the highlights of my political career - the opportunity to be there at a point where hopefully we can make a difference."

He said it was important Syria's President Bashar al-Assad and Assad's domestic opponents all signed up to the ceasefire.

"Don't underestimate both the influence the Russians have with Assad himself and the real desire both the Russians and the Americans have to find a solution."

A ceasefire in February had lasted for about two months and Key said if the current agreement lasted longer, countries could start working on a longer term solution.

"New Zealand's position from a diplomatic perspective is we don't think Assad is part of the long-term future of Syria, we want to see transition there. But it's got to happen in an orderly way and we understand and respect that."

He said the US and Russia were the relevant players in that respect and the fact they had agreed on a ceasefire would help.

"We know over 400,000 people have been killed and nearly half the Syrian population displaced as a result of the tensions in Syria. That can't go on. So the people of Syria need help and support."

Key will also continue to lobby for Helen Clark to be UN Secretary General in the lead-up to the next straw poll in late September. He believed Clark's chances were "less than 50 per cent but certainly not zero as some people have tried to indicate".

"Her biggest problem is the core issue that the Russians are just adamant it should be an Eastern European and that's what's made her life a bit challenging, I think."

A more formal poll using coloured ballots is scheduled for early October when the vetoes of the five permanent members will be clear.

"This will get very interesting when ultimately the permanent five [members on the Security Council] either decide or decide not to exercise the veto. Once that happens, a lot of things can change. She's always held the view to win she needs to be the compromise candidate."