Putin also voiced concern about US plans to build a missile defence system in eastern Europe, probably Poland and the Czech Republic, and the expansion of Nato as possible challenges to Russia.

"The process of Nato expansion has nothing to do with modernisation of the alliance or with ensuring security in Europe," Putin said.

"On the contrary, it is a serious factor provoking reduction of mutual trust."

He also dismissed suggestions that the European Union and Nato had the right to intervene alone in crisis regions.

"The legitimate use of force can only be done by the United Nations, it cannot be replaced by EU or Nato," he said.

On the missile defence system, Putin said: "I don't want to accuse anyone of being aggressive" but suggested it would seriously change the balance of power and could provoke an unspecified response.

"That balance will be upset completely and one side will have a feeling of complete security and given a free hand in local, and probably in global, conflicts...," he said.

"We need to respond to this."