The Prime Minister arrived in Brazil on a trade boosting mission - opening a new digger factory amongst other things. Mr Cameron said he wants Britain to be linked to the world's fastest growing economies.
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The singer had been tweeting in support of migrants when she was bombarded with abusive messages.
Ministers are reportedly considering plans in a bid to lower inward migration.
In a tweet on Saturday, the US president didn't give a reason for his absence but said he wished"everyone well and have a great evening".