NATO and Russia failed on Thursday to narrow their differences over the alliance's missile defense system in Europe, but talks will continue in a bid to reach a deal by May next year, the NATO chief said.

"It's no secret that differences remain on how to organize our cooperation in this area. But the sort of intensive dialogue we've had today shows that we are committed to finding a way forward," NATO Secretary General Anders Fogh Rasmussen said after the meeting of the NATO-Russia Council.

"We do not agree yet. But we all agree that it is important to keep on trying. To keep on talking. And to keep on listening to each other's concerns," he said.

Rasmussen insisted that the missile defense system is not directed against Russia, who is not an enemy, but a partner of NATO.

However, the oral promises apparently failed to ease Moscow's deep concerns that the system poses a real threat to its nuclear deterrence and national security.

Russian Foreign Minister Sergei Lavrov told reporters that NATO should listen to Russia's concerns seriously and provide a legal guarantee that Russia will not targeted.

"Apart from general remarks about trust and not targeting systems against each other, we need legally-binding arrangements, because good intentions come and pass," he said.

Rasmussen said that NATO and Russia should reach an agreement on missile defense by the alliance's next summit in May 2012, when the system will acquire interim operational capability.

"It would be quite nature that we reach an agreement with Russia at the same time...The first time horizon would be and should be May next year," he said.

Tensions have risen between NATO and Russia around missile defense. Last month, Russian President Dmitry Medvedev warned that Russia would deploy missiles against NATO's anti-missile shield, if the two fail to reach an agreement.