Russia is using nuclear threats to try to intimidate Europe, Nato's secretary general has warned.
Jens Stoltenberg said the organisation was not seeking a new Cold War with Moscow, but moving military assets to Eastern Europe as a precaution.
"Russia is a nuclear power, and a nuclear power which is using nuclear rhetoric to try to intimate other European nations, so we take this seriously.
"I don't see any imminent threat, but I see a stronger Russia. I see a Russia which is more assertive, and a Russia which has been willing to use force against non-Nato European countries.
"We don't seek confrontation with Russia, we don't want a new Cold War, actually we will continue to strive for a more cooperative and constructive relationship with Russia, but we have to do that based on collective defence deterrents," he told BBC Radio Four's Today programme.
Mr Stoltenberg said Nato had a "problem" with some member states not paying enough for their defence.