Almost 75,000 migrants and refugees have arrived in Greece by sea since the start of 2016, the UN says.
Reacting to news that Nato will deploy ships in the Aegean Sea to combat people-smugglers, a Ministry of Defence spokesperson said:
Nato's mission in the Aegean Sea will not be able "stopping or pushing back refugee boats", Nato's secretary-general has said.
Jens Stoltenberg said ships will contribute "critical information" to help the Turkish and Greek coastguard tackle human trafficking and criminal networks.
He also said Nato would step up surveillance of the Syrian-Turkish border.
The move to deploy ships follows a request from Germany, Turkey and Greece.
Thousands of refugees have already arrived in Greece by sea since the start of the year.
Nato has agreed to start patrols in the Aegean Sea to slow the flow of refugees travelling to Europe and to tackle people smuggling.
"It is important that we now act quickly," Ursula von der Leyen, German defence minister, told reports after a meeting in Brussels.
Nato could launch patrols in the Aegean Sea to deter people-smugglers taking migrants from Turkey to Greece, the US secretary of defence said.
Ash Carter said Nato allies were considering the move after a request from Germany, Turkey and Greece to help slow the refugee flows.
"There is now a criminal syndicate that is exploiting these poor people and this is an organised smuggling operation," Carter told a news conference during a meeting of Nato defence ministers in the Belgium capital Brussels.
"Targeting that is the way that the greatest effect can be had in the humanitarian dimension," he said.
Nato has urged Turkey to be "proportionate" in its response to terrorist attacks even though it has suffered from crises in the Middle East more than any other Nato member.
Speaking in Norway after a twin suicide bombing in the Turkish capital Ankara which killed at least 97 people, Secretary-general Jens Stoltenberg said: "They (Turkey) have seen several terrorist attacks.
"They have the right to defend themselves, but I of course expect Turkey to be proportionate in the way they respond."
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The UK is to send up to 1,000 troops to a high readiness force and deploy four RAF Typhoon jets for air policing in the Baltic States to boost NATO’s collective security, the Defence Secretary has announced.
Michael Fallon says the UK will be the lead nation in the Very High Readiness Joint Task Force (VJTF) in 2017 and then on rotation thereafter. This will see the UK contributing manpower to two regional headquarters in Poland and Romania and to force integration units in the three Baltic States, Poland, Romania and Bulgaria.
The UK will also send four RAF Typhoon jets to support the NATO Baltic Air policing mission again in 2015.
NATO’s credibility in the face of the security challenges we face depends on everyone playing their part to implement the decisions taken at Wales last year.
The Readiness Action Plan demonstrates the Alliance’s commitment to reinforce our collective defence but strong words must be backed up with firm action. That is why I am delighted to announce that the UK will lead the VJTF in 2017 and contribute to the Baltic Air Policing mission again in order to put the Plan into practice.