The US President's Chief of Staff, Denis McDonough, has said that the election of Hassan Rouhani to the Iranian presidency is a "potentially hopeful sign".
He added that Rouhani "will find a partner in us" if he lives up to his nation's obligation to "come clean" on its nuclear programme.
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Guillier conceded a "severe defeat" defeat to his supporters as the result came in.
The outage struck Hartfield-Jackson Atlanta International Airport at around 1pm local time, stopping all outgoing flights.
It will be a chilly day for many parts with the highest temperatures, about 10 Celsius (50F) in the far northwest.