KABUL, Afghanistan — The mud house where insurgents began digging a lengthy tunnel that at least 488 inmates used to flee an Afghan prison had been searched about 2 1/2 months before by security forces who failed to notice anything amiss, authorities said Tuesday.

Afghan Justice Minister Habibullah Ghaleb faulted security forces for overlooking the nearly quarter-mile tunnel and failing to prevent the escape on Sunday night and Monday morning from Kandahar’s Sarposa prison. Authorities estimate that militants spent five months digging the tunnel.

“”Earth or soil dug out of the tunnel must have been moved and should not have been missed by the eyes of the security forces,”” Ghaleb said in a report to President Hamid Karzai.

But Ghaleb also blamed foreign troops, noting that Canadian forces had been stationed at the prison in the past, and that U.S. troops had been building living quarters and judicial offices at the prison for the past four months even as the tunnel took shape beneath them.

Ghaleb said he suspects escapees had help from someone inside the prison, since they managed to unlock multiple cells to reach the tunnel, which ended within a single cell. The escape went on for more than four hours.

Afghan authorities and foreign troops launched a manhunt for the escapees but had only captured 65 as of late Tuesday, according to Tooryalai Wesa, the governor of Kandahar province.

The Taliban, who consider the escape a major victory, had claimed 541 inmates fled through the tunnel and were later driven to safe houses.

Afghanistan’s government has launched a full investigation into the escape, the second in three years at Sarposa. In 2008, about 1,000 prisoners including Taliban fighters escaped from Sarposa after a truck bomb attack at the jail’s gates.