The United States understood, however, when they transferred custody of the detainees to British authorities that they would be released if no charges could be brought against them, said Lieutenant Commander Flex Plexico.
"We continue to believe that these individuals pose a significant threat," he said. "British authorities have assured us that they will take necessary steps to address the threat posed by these individuals."
He would provide no detail on the steps the British authorities agreed to take.
Moazzam Begg, Richard Belmar, Martin Mubanga and Feroz Abbasi were flown back to Britain Tuesday after up to three years in detention at Guantanamo Bay.
They were questioned Wednesday by members of a police anti-terrorist unit, then released without charge, police told AFP.