* Britain, wary of EU, opposes any mandatory quotas
* Germany, France and Italy would receive most refugees
* Britain, Ireland and Denmark given opt-outs (Edits, adds British, Irish, Danish comment)
By Robin Emmott and Alastair Macdonald
BRUSSELS, May 13 (Reuters) - The EU announced a plan on Wednesday to distribute asylum-seekers more fairly around its member states and take in 20,000 more refugees, but Britain's newly re-elected Conservative leaders rejected any quota system imposed from Brussels.
Shocked by thousands of deaths among people trying to reach Europe from North Africa across the Mediterranean, the European Union is trying to put in place a fairer way to resettle asylum-seekers at a time when anti-immigration parties are on the rise.
Italy and other southern European countries are clamouring for help to relieve the influx. Germany, Sweden, Austria and others are favoured destinations for migrants who, once ashore, travel across the bloc's open borders to claim asylum. Those states have asked to spread those requests more evenly.
The European Commission stressed that it was proposing only a provisional emergency response to an accelerating movement that saw over 600,000 people, many fleeing hunger and war in Africa and the Middle East, seek refuge in the EU last year.
But the proposal of mandatory quotas, based on states' population and national income but also on unemployment levels and past acceptance of refugees, has put some governments on the defensive, notably Britain, where Prime Minister David Cameron was re-elected on a promise to curb immigration from the EU before holding a referendum by 2017 on quitting the bloc.
Even before the EU announced its plan, interior minister Theresa May wrote in a newspaper column that London would use its exemptions from EU migration laws to stay out of the system. "Such an approach would only ... encourage more people to put their lives at risk," she wrote.
Frans Timmermans, the Dutch deputy head of the EU executive, who is expected to play a key role in negotiating with Cameron ahead of the British referendum, was visibly irritated by the suggestion that the Commission's plan was counter-productive.
"I have the highest regard for British intelligence but I'm not sure Theresa May had read all the proposals we've made," he told a news conference after presenting the plan.
He noted that it also included tightening border controls, working with African states to curb people smuggling networks, naval operations against trafficking vessels and doing more to ensure people were deported if their asylum claim was rejected.
"I wonder how anyone can maintain that this would make the situation worse," Timmermans said.
Ireland also opted out but plans to take in as many refugees as the system would have allocated to it. Denmark, the third state enjoying exemptions, said it would follow its own policy.
Without naming Britain, Germany's migration minister accused London of running scared of right-wingers: "The answer to rising numbers of refugees cannot be to opt of a joint asylum policy from fear of strengthening populists," Aydan Ozoguz said. "Each member state has a legal and moral obligation to do its duty."
Some 51,000 migrants have entered Europe by crossing the Mediterranean sea this year, with 30,500 coming via Italy. About 1,800 have drowned in the attempt, the U.N. refugee agency says.
European Commission President Jean-Claude Juncker argued that Europe needed immigrants to refresh its ageing population.
Britain wants the bloc to do more to target people smugglers in Libya. EU foreign ministers are expected to approve on Monday plans for a naval and air mission to seize smugglers' vessels. But a programme with a wide scope is waiting for a U.N. Security Council resolution the EU hopes it can have by Monday.
The resolution would authorise the EU to intervene on the high seas, in Libyan territorial waters and coastal areas. (Additional reporting by Philip Blenkinsop and Francesco Guarascio; Editing by Louise Ireland and Crispian Balmer)
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