Bradley Manning was pictured earlier arriving at Fort Meade in the US state of Maryland, where he will face a military judge.
His sentencing is expected in the next few minutes.
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A spokesperson said Rory Stewart's remarks were in line with the British government’s stated position.
The minister's intervention will come a week after Trump decertified the landmark agreement claiming it was not in the US national interest.
Scientists suggest that in 30 years antibiotic resistance will likely kill more people globally than cancer and diabetes combined.