US soldier Bradley Manning has been sentenced to 35 years in prison.
Manning, 25, was convicted last month of espionage, theft and other charges in the biggest leak of classified information in American history.
He was acquitted of aiding the enemy, the most serious of the charges against him.
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British soldiers will join troops from some 30 countries who work in the country.
The demand comes after the Prime Minister urged a "grown up" relationship between her government and the devolved administrations.
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