It has rejected Russia's explanation as to why its fighter jets violated Turkish airspace in recent days.
Tension in the region is growing with reports of a Russian troop build up on several fronts in Syria.
Just one week in and Russia's bombing campaign in Syria is mired in controversy.
NATO secretary-general Jens Stoltenberg refusing to accept its account of an incursion into Turkish airspace as a fleeting mistake caused by bad weather.
"This is a serious violation of the airspace. And actually there were two violations during the weekend. So that just adds to the fact this doesn't look like an accident. The violation lasted for a long time compared to previous violations of airspace we have seen other places in Europe. And therefore we take this very seriously."
There were even stronger words from the Turkish President, Recep Tayyip Erdogan.
"NATO has taken a very tough line against this and I am convinced that it will continue to do so. Any aggression against Turkey is an aggression against NATO."
That is not the only concern.
Jens Stoltenberg says NATO is alarmed by the substantial Russian military build-up in Syria.
"I will not go into any specific numbers but I can confirm that we have seen a substantial build-up of Russian forces in Syria, air forces, air defences but also ground troops."
It is fuelling speculation of an impending ground offensive.
It could include Syria's army fortified by forces from Russia, Iran and the Lebanese militia Hezbollah.
Russian targets also remain a matter of deep contention.
The United States is accusing Russia of trying to shift the balance of power in Syria by repeatedly striking outside IS and Syrian government-controlled areas and into rebel territory.
Russia emphatically claims that it is attacking IS targets.
John Kerry, US Secretary of State is sceptical.
"If Russia's intent is to focus more on shoring up Assad and his regime, rather than legitimately narrowing the focus to ISIL and its affiliates, that will make it impossible to find the political solution that they say they want."
There are mixed messages too about whether Russian airstrikes hit IS targets in Palmyra, adjacent to its ancient ruins.
One Russian state media outlet denied the strikes, while another reported that Russian jets had killed IS millitants.
There are concerns the displays of military power from both sides reflects longstanding differences between Russia and the United States playing out, not only in the United Nations but on the battlefield in Syria.
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