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Why are migrants risking their lives to reach Europe?

20 April 2015 Last updated at 16:45 BST

The United Nations says much more must be done to help thousands of migrants trying to reach Europe by boat.

UN figures say 13,500 migrants have been rescued trying to reach Europe so far this year and around 35,000 have arrived from Africa in 2015.

A boat carrying up to 900 people sank off the north African coast on Saturday. Authorities say 28 people were rescued; but many more died.

European leaders are meeting this week to try to work out what to do.

Martin's got more on this difficult story.