NATO and Russia have started talks on the possibility of building an anti-missile defence system in Europe, NATO chief Anders Fogh Rasmussen said Thursday.

"We had the first discussions on this issue in the NATO-Russia council" on Wednesday, Rasmussen told a news conference during a one-day visit to Sofia.

"We have prepared further discussions from now until the NATO summit in Lisbon," he said.

"So we had started the discussions and obviously there are a ... number of issues to be discussed and clarified before concrete cooperation can start. But we have already started that process," the NATO chief said.

NATO members are expected to decide whether to give the go-ahead to a missile defence system at a summit of the transatlantic alliance in Lisbon in November.

Rasmussen said NATO hoped to develop an effective system covering not only those locations in Europe where allied troops are deployed, but all of the 28 member countries, whose combined population totals 900 million.

And NATO was ready to cooperate with Russia in missile defence, he insisted.

"Politically, it would be a clear demonstration that the missile defence system is not directed against Russia. And militarily, it would also make the whole system more effective," he said.

"So there are many good reasons to cooperate with Russia in that respect," Rasmussen said.

Anti-missile defence systems already in place within the NATO alliance fall under a US shield that has missile interceptors in the United States, Greenland and Britain.

Plans for it to be extended into eastern Europe have raised serious concern in Russia, which fears an extension of the US missile shield project in Europe could upset the conventional and nuclear balance to its own detriment.

Rasmussen played down the Russian fears, saying the system was rather planned to counter threats coming from Iran.

"If Iran really acquires a nuclear capacity, it might constitute a real threat to NATO allies," he said.

NATO was following closely the issue of Iran's nuclear activity even if it was not directly involved, he said.

Commenting on a recent deal between Iran, Turkey and Brazil to swap low enriched uranium for nuclear fuel, Rasmussen said: "This new tripartite agreement will not have any impact on our plans as regards the missile defence system."