KABUL - Afghan President Hamid Karzai accused the United States on Sunday of breaching a pact to hand over the main US military prison at Bagram Airbase and its inmates to Afghan control, after meeting Washington's top envoy to the region.

In a row which could complicate already thorny negotiations over the future US military presence in the country, Karzai told US Special Envoy to Afghanistan and Pakistan Marc Grossman any delay to the handover was "a serious violation" of a strategic agreement between the allies. "The people of Afghanistan consider the issue of prisons and detention of their fellow citizens a matter of their national sovereignty," said a statement released by Karzai's office after the president met Grossman at his garden palace in Kabul.

The US handed over the high-security prison and around 3,000 suspected Taliban fighters to Afghan control over a six-month period ending on September 10, but did not transfer 600 or so detainees captured after the memorandum was signed. The prisons deal, which took almost a year to conclude, helped lay the ground for a separate strategic pact framing US development aid and support to Afghanistan for a decade after the withdrawal of most foreign combat troops in 2014. It also prepared the way for yet another round of negotiations on a status-of-forces deal covering US basing and troop numbers in Afghanistan after the NATO pullout, likely including more military advisers and special forces.

But Karzai's unhappiness with progress on the Bagram deal could put a chill over those talks, undermining public support for Karzai and his already unpopular government. "The continued holding of Afghans in American custody runs in contradiction with the spirit of mutual friendship and the provisions of the bilateral strategic partnership agreement," Karzai's office said.

Afghanistan has long sought control of the sprawling prison, which has been likened to Guantanamo in Cuba and Abu Ghraib in Iraq for its association with abuse of inmates. "Ambassador Grossman made clear in his discussion with the President that the United States fully respects Afghan," the US embassy in Kabul said in a statement.

US troop numbers in Afghanistan have fallen from a peak of nearly 100,000 at the start of this year to around 68,000 by October. Around 100,000 foreign troops remain in the country.