Lawyers for the sponsors of California's same-sex marriage ban have filed an emergency motion asking the U.S. Supreme Court to stop gay weddings, reported Associated Press.
The supporters of gay marriage say the federal appeals court "acted prematurely" by lifting an injunction which prevents the unions.
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The suspect, 35-year-old Willie Corey Godbolt, has been arrested and was being treated for a gunshot wound in hospital.
Mohanna Abdhou, known as Montana, was out with friends when two attackers cycled up to them and opened fire in Brent, north-west London.
The US president tweeted that Mrs May gave him "full details" of the incident during talks while he attended summits in Europe.