Nato ships are being deployed to the Aegean sea to deter people-smugglers taking migrants from Turkey to Greece, Nato chief Jens Stoltenberg says.

The announcement followed a request from Turkey, Germany and Greece at a defence ministers' meeting in Brussels.

Mr Stoltenberg said the mission would not be about "stopping or pushing back refugee boats".

Nato, he said, will contribute "critical information and surveillance to help counter human trafficking".

The decision marks the security alliance's first intervention in Europe's migrant crisis.

US defence secretary Ashton Carter earlier said that targeting the "criminal syndicate that is exploiting these poor people" would have the greatest humanitarian impact.

The decision was made to help Turkey and Greece "manage a human tragedy in a better way than we have managed to do so far," Mr Stoltenberg, Nato Secretary General, said.