Around 100 migrants seeking to reach Italy from north Africa have been rescued by a Royal Navy warship.
Defence Secretary Michael Fallon confirmed HMS Enterprise took part in the rescue on Sunday amid concerns a new Nato operation in the Aegean Sea could neglect other routes into Europe.
A Royal Navy amphibious landing ship - Mounts Bay, which carries a Wildcat helicopter as well as Royal Marines and medics - is expected to start operations in the Aegean Sea soon.
Addressing the route from Libya to Italy, Mr Fallon told MPs: “HMS Enterprise is still on station in the Tyrrhenian Sea and indeed just yesterday rescued around 100 people.
“What’s important in this, I think, is to begin to establish a policy of return so there is less incentive for migrants to attempt these extremely dangerous crossings and less incentives for the criminal gangs to make money out of them doing so.”
Two further border cutters will also join the Nato mission in the Aegean Sea, which seeks to identify people smugglers and reduce the number of migrants travelling from Turkey to Europe as the Syrian civil war continues.
Liberal Democrat former minister Alistair Carmichael warned more people have died on the sea route from Libya to Italy than in the Aegean Sea, as he questioned how the new operation will affect resources in the region.
Mr Carmichael, raising an urgent question in the Commons, asked Mr Fallon: “What impact does the Government think that this action will have on the flow of refugees elsewhere?
“I’m sure you’ll be aware that last year 35,000 people came to Europe through Russia - and what will be the impact on that land route if the sea route is to be closed down?
“And what will this mean for the deployment of resources elsewhere in the Mediterranean, in particular assisting those travelling from Libya to Italy?
“You’ll be aware that the coastguard cutters were deployed on that route last year. Will they be available to help those who get into difficulty on that route, which has seen many more deaths by drowning than that in the Aegean Sea?”
Earlier, the Lib Dems’ home affairs spokesman voiced concerns over the lack of a strategy.
Mr Carmichael said told Mr Fallon: “It’s referred to today in the press as being a war against people traffickers.
“If we are to win that war then I feel what we need is to do is to cut off the supply to the people traffickers of those who are desperate enough to pay to use them.
“Of course that means in the longer term getting peace in their countries of origin, but in the short to medium term surely that means a series of safe and legal routes into Europe, expansion of the refugee families scheme and introduction of humanitarian visas?”
He asked Mr Fallon if those refugees who are intercepted in the Aegean Sea will be returned to Turkey, adding: “Does that not run contrary to the principle of non-refoulement, which is at the centre of international refugee law?”
In reply, Mr Fallon told Mr Carmichael: “So far as the creation of safe routes is concerned, I’m not convinced that establishing routes as safer than others will do anything to reduce the flow.
“On the contrary, I think we need to increase the capacity - particularly of the Turkish authorities and the Turkish coastguard - to be able to intercept these boats before they set off on what is a very, very dangerous crossing.”
Mr Fallon said for a boat intercepted in Turkish waters by the Turkish authorities, potentially alerted by the Nato helicopters, there is a “greater chance the Turkish coastguard will return those particular boats to the Turkish side”.
He went on: “If they are intercepted in international Greek waters then they’re more likely to be taken to the Greek reception points.”
Mr Fallon then confirmed HMS Enterprise’s recent rescue mission.
Shadow defence minister Toby Perkins said the UK’s “small” contribution in the Aegean Sea in response to a “gigantic” crisis illustrated the scale of cuts to the Navy since the Tories came to power.
The Labour frontbencher said: “Whilst we welcome the role that RFA Mounts Bay will play, it is a small contribution to a gigantic crisis and is maybe a reminder of how the Royal Navy surface fleet has been reduced by a sixth since 2010.
“I’d like to ask you whether you feel that our naval resources are too stretched to play a large role in this operation?
“And can you tell us whether you believe the three Border Force vessels in the Aegean are there and not protecting UK seas because of the reduction in naval capacity caused by the 2010 SDSR (Strategic Defence and Security Review)?”
Mr Perkins said Nato’s assistance to the EU shows the importance of Britain’s membership of the union.
He said: “Nato joining what’s previously been an EU role further demonstrates the extent to which our role in the EU enhances our global security.
“Do you agree with the Prime Minister that leaving the EU may bring the refugee camps to the streets of Britain and what more can you tell us about how you believe the EU helps to keep Britain safe?”
Replying, Mr Fallon said Mounts Bay would operate alongside five other ships from Germany, Greece, Canada, Italy and Turkey as he urged other countries to help the effort.
“Of course there are 22 other members of Nato and I hope they too will be considering what contribution they can make,” he said.
The Defence Secretary said the new deployment “perfectly illustrates” the need for Britain to be a member of both the EU and Nato to ensure security.
Mr Fallon said: “The mission in the sea between Libya and Italy is a European Union mission because it may need the legal authorities that the European Union can add in dealing with the new Libyan government.
“The force deployed in the Aegean is a Nato mission because of course it involves a ship of the Turkish navy and is dealing largely with migrants from Turkey, which is a member of Nato, perfectly illustrating that we need to be members of both Nato and the European Union and that being members of both gives us the best of both worlds.”
The EU has confirmed that it will provide Turkey with three billion euro over two years to help the country deal with the refugee crisis, with the UK contributing 327 million euro (£250 million).
Home Affairs Select Committee chair Keith Vaz said the money was “key” in helping the Turkish authorities stop people traffickers sending dangerous boats full of vulnerable people to sea.
The Labour MP said: “As you know, a million migrants have entered the EU last year, 885,000 through Greece, and Europol told us last week that 90% of those who have entered have come as a result of assistance from criminal gangs.
“We are in this place because of the failure of the EU and in particular Frontex to deal with these gangs properly.
“There has been no alternative to the business model that you have described, that the traffickers are adopting.
“Do you agree with me that the critical country here is Turkey and the issue is to stop the boats leaving in the first place?
“And what is key to that is giving Turkey the resources that the EU promised, the three billion (euro), to get them to assist with this difficult problem.”
SNP defence spokesman Brendan O’Hara called on Mr Fallon to update the Commons on UK military strategy in Syria and to accept more lone child migrants.
“As this crisis worsens, the need for the UK Government to commit to take 3,000 unaccompanied vulnerable and displaced children becomes ever more of an urgent priority,” he said.
“And further to that, and looking at the bigger picture, when will you update this House as you promised you would do on the Government’s military strategy in Syria?”
Mr Fallon said the Government has already committed to taking refugees from camps in and around Syria and taking some unaccompanied children identified by the UNHCR in Europe.
Labour’s refugee taskforce chair Yvette Cooper said the Government must help refugees who are already in Europe.
“For those that have already arrived in Greece, there are 13,000 of them now at the Macedonian border in terrible wet and damp and cold conditions, children with bronchitis,” she said.
“You have said that the British Government won’t do anything to take any of them - where do you think those 13,000 people should go?”
After the statement was repeated in the upper house, former Lib Dem leader Lord Ashdown of Norton-sub-Hamdon accused the Government of “abandoning” migrants once they had been rescued.
Lord Ashdown said the latest moves were welcome, but the Government had a discredited policy.
“Her Majesty’s Government’s policy is to rescue such refugees as they find in danger with their lives, and then to abandon them because Her Majesty’s Government will not take a single one of the refugees now fleeing for their lives from the Syrian battlefields, but we are perfectly happy to criticise Europe for not being able to cope with a million,” the Lib Dem peer said.