Afghan President Hamid Karzai on Saturday demanded that Britain hand over within two weeks more than 80 prisoners of war being held in a British base in the south, saying the detention was against Afghan law and a breach of sovereignty.
The issue of prisoner transfers is an irritant in the relationship Karzai between and his Western backers, and has become more pronounced as the NATO-led international force prepares to pull out most of its troops by the end of next year.
Last month, a British legal firm said the detention of up to 85 Afghans for as long as 14 months in the British-controlled Camp Bastion in Helmand province was in breach of British and international law.
The British government has cited concerns about Afghanistan's treatment of detainees and denied that claim.
On Saturday, Karzai's national security adviser, Rangin Datfar Spanta, spoke to the British Embassy in Kabul and asked for the detainees to be handed over by June 22, said a statement from Karzai's spokesman, Aimal Faizi.
"Continuing the detention of Afghan nationals by British forces will be a violation of our national sovereignty and our country's laws," Faizi said.
British officials in London had no immediate comment.
Foreign rights groups occasionally accuse the Afghan state of using torture and abuse, while Kabul says Western nations rely on questionable international legal principles to detain Afghans without access to Afghanistan's courts.
Numerous countries fighting in the U.S.-led war in Afghanistan continue to hold Afghan detainees. Last month Australia, which operates a force in the southern province of Uruzgan, announced it was suspending transfers of prisoners to an Afghan facility due to allegations of mistreatment.
In November, British Defence Secretary Philip Hammond imposed a ban on transferring suspects to Afghan forces due to concerns over ill treatment.
He added that the detainees were suspected of killing British troops and planting roadside bombs.
Camp Bastion houses around 30,000 staff and is the largest British military base in Afghanistan.
On May 31, the United Nations anti-torture watchdog urged Britain to widen and speed up investigations into alleged torture of detainees in Iraq and Afghanistan by British troops, and prosecute those responsible.