Home Secretary Theresa May on Wednesday criticised the EU's approach to stemming the flow of migrants crossing the Mediterranean into Europe, saying that by not sending economic migrants back, the bloc was encouraging them to travel.

International focus on the issue of migration into Europe has been sharpened by a series of disasters in the Mediterranean in which hundreds of migrants from North Africa have drowned after attempting to cross the sea in unsafe vessels.

After briefing the United Nations Security Council on plans to deal with such migration, the EU's foreign policy chief Federica Mogherini on Monday said no refugees or migrants intercepted at sea would be sent back against their will.

Home Secretary May criticised Mogherini's statement.

"Such an approach would only act as an increased pull factor across the Mediterranean and encourage more people to put their lives at risk," she wrote in an article in the Times newspaper.

About 1,800 migrants have perished in the Mediterranean this year, the United Nations refugee agency said. Some 51,000 have entered Europe by sea, with 30,500 coming via Italy, fleeing war and poverty in Asia, Africa and the Middle East.

On Tuesday Britain said it would opt out of any EU plan to resettle refugees using country quotas, saying it preferred to focus its efforts on tackling people traffickers instead.

"We must - and will - resist calls for the mandatory relocation or resettlement of migrants across Europe. Such an approach would only strengthen the incentives for criminal gangs to keep plying their evil trade," May said on Wednesday.