NATO leaders gathered in Warsaw this week determined to show unity and resolve in the face of an ever-more defiant Russia, but disagreements about how best to handle their giant neighbour bubbled just below the surface.

Relations between the Western military alliance and Moscow have hit a post-Cold War low following Russia's annexation of the Crimean peninsula and its support for separatists in Ukraine.

Both sides have been flexing their military muscles ever since, accusing each other of sabre-rattling and provocations.

In Warsaw, NATO leaders layed the blame at Moscow's feet.

"Russia's aggressive actions, including provocative military activities in the periphery of NATO territory, ... are a source of regional instability, fundamentally challenge the alliance, have damaged euro-Atlantic security, and threaten our long-standing goal of a Europe whole, free and at peace," they said in the communique issued at the end of their talks on Saturday.

The 28 leaders cleared the way for military reinforcements all along NATO's eastern flank, with four rotational battalions headed next year to Estonia, Latvia, Lithuania and Poland - the countries that have felt most threatened by Russia's actions in Ukraine.

"This finally shows ... that NATO went out from their offices and paper plans to the field and became a real defence organization," Lithuanian President Dalia Grybauskaite jubilantly said in Warsaw.

But others have called for restraint, amid fears that the tensions will boil over into military incidents such as the 2015 downing of a Russian jet by NATO member Turkey at the Syrian border.

"For France, Russia is not an enemy, is not a threat," French President Francois Hollande said in Warsaw.

"What we shouldn't do now is further inflame the situation with loud sabre-rattling and war cries," German Foreign Minister Frank-Walter Steinmeier told the German tabloid Bild last month.

Germany, the EU's leading power, has been among those pushing for NATO to rekindle dialogue with Russia. Ambassadors from the alliance are scheduled to meet their Russian counterpart Alexander Grushko in Brussels on Wednesday to inform Moscow about the decisions taken at the Warsaw summit.

"We do not want a new Cold War," Stoltenberg said. "We will continue to strive for a meaningful and constructive dialogue with Russia."

British Prime Minister David Cameron said there was "very strong consensus" at the summit dinner on Friday on this, but also on the fact that "we need to have that dialogue from a position of unity and strength over the issue of Ukraine."

"Boundaries are being redrawn in Europe by force, by one power, and Europe and NATO must stand strong against that," he added.

Ukrainian President Petro Poroshenko, who held talks with the NATO leaders at their summit, said there was "full support demonstrated by all member states," notably when it comes to the question of sanctions on Russia.

The European Union - most of whose members also belong to NATO - this month prolonged by six months its economic sanctions on Moscow. The bloc's leaders are expected to discuss the future of their relationship with Russia later this year.

Steinmeier said in Warsaw that he does not expect the NATO dialogue with Moscow to be "easy." The summit will not improve the atmosphere, not least because it was held in a country that used to be under the Soviet Union's sphere of influence.

"Almost every NATO summit is seen by Russian diplomats and official media as a hostile event," said Alexander Baunov of the Carnegie Moscow Center think-tank. "The agenda of the 2016 NATO summit should provoke the Kremlin's anger."

Former Soviet president and Nobel Peace Prize laureate Mikhail Gorbachev on Saturday accused NATO of war-mongering.

"From a Cold War NATO is going over to the preparations for a hot [war]," Gorbachev told the Interfax news agency. "They are only talking about defence, but essentially they are making attack preparations."

Baunov, however, predicted that the tensions between Moscow and the West would eventually cool down.

"Both sides - Russia and NATO - feel that ... some detoxification of relations should be undertaken," he said. "There is a general feeling that the confrontation should not be heightened further."

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