Audrey Young in New York

John Key is set to land in the centre of a diplomatic crisis between the United States and Russia during leaders' week at the United Nations over the truce in Syria.

Tensions between Russia and the US escalated over the weekend, just days before the Prime Minister is due to chair a Security Council meeting on Syria.

The US admitted yesterday it had bombed Syrian Government troops but it had believed the targets to be Isis - the death toll has been put at 62.

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Russia's ambassador to the UN, Vitaly Churkin, told reporters the timing of the strike was "significant and suspicious" and suggested it could have been timed by the Pentagon to disrupt further discussions on implementation of the truce.

"Who is in charge in Washington. Is it the White House or the Pentagon?"

US ambassador to the UN Samantha Power said the US regretted the loss of life.

But she riled the Russians by walking out of a Security Council meeting on Syria calling the Russian ambassador's protestations a "stunt".

"Even by Russia's standards, tonight's stunt, a stunt replete with moralism and grandstanding, is uniquely cynical and hypocritical," she told reporters at the UN.

"Since 2011, the Assad regime has been intentionally striking civilian targets with horrifying, predictable regularity."

MORE: Foreign Minister Murray McCully speaks to Mike Hosking about Syrian war

New Zealand is chairing the Security Council this month, which is why Key will take the reins on Thursday, and Foreign Minister Murray McCully has chaired some sessions.

New Zealand's ambassador to the UN, Gerard van Bohemen, was in the chair for yesterday's volatile session on Syria.

The truce was negotiated between US Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov, both of whom were due to arrive in New York at the weekend.

Russia has supported the Syrian Government in the five-year civil war and the United States has supported the anti-government rebels.

READ MORE: Barry Soper: Key's anticipated moment in the UN spotlight

Under the terms of the truce, the Syrian Air Force strikes are restricted and if the truce holds for a week, the US and Russia will begin to co-operate on military action against Isis and Jabhat Fateh al-Sham (formerly known as al-Nusra Front).

McCully said the developments over the weekend "put our presidency at the centre of some pretty challenging times, but that's what we signed up for".

Key is due to arrive early today New Zealand time.