NATO allies have "significant differences" with Russia over its demands for new security rules in Europe, but are ready to meet Kremlin envoys again, the alliance's chief Jens Stoltenberg said Wednesday. 

"There are significant differences between NATO allies and Russia on these issues, and the differences will not be easy to bridge," he said after talks with Russia at NATO headquarters in Brussels. 

"But it is a positive sign that all NATO allies and Russia sat down around the same table."

Speaking after a meeting of the revived NATO-Russia Council, Stoltenberg said the allies had agreed to hold a series of meetings with Moscow on a variety of strategic issues.

"Russia was not in a position to agree on that proposal. They didn't reject it either, but the Russian representatives made it clear that they needed some time to come back to NATO with an answer," he said. 

Stoltenberg warned, however, that Russia would have no veto over any bid by Ukraine to join NATO and called for a "de-escalation" in Russia's military build-up on its neighbour's border.

"Ukraine as a sovereign nation, Ukraine has the right to self defence Ukraine is not a threat to Russia," he said.

"It is Russia that is the aggressor. It is Russia that has used force and continues to use force against Ukraine," he said.

"And then they're building up with around 100,000 troops, artillery, armour, drones, tens of thousands of combat ready troops and threatening rhetoric -- that's the problem."