US Secretary of State John Kerry has arrived in Vienna for talks with foreign ministers about Tehran's nuclear program.
Iran and the six powers- Britain, the US, France, Germany, Russia and China- aim to reach a long-term deal to end the decade-old nuclear standoff by July 20.
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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".