WASHINGTON (AP) — One in five terror suspects released from the Guantanamo Bay prison has returned to the fight, according to a classified Pentagon report expected to stoke an already fierce debate over President Barack Obama’s plan to close the military prison.

The finding reflects an upward trend on the recidivism rate, although human rights activists who advocate closing the prison have questioned the validity of such numbers.

Early last year, the Pentagon reported that the rate of released detainees returning to militancy was 11 percent. In April, it was 14 percent. The latest figure was 20 percent, according to a U.S. official, who spoke on condition of anonymity because the report had not been declassified and released.

Critics of the reports say there is so little information in the assessments that they are nearly impossible to verify independently. Civil rights advocates say the number of fighters suspected of or confirmed as returning to the battlefield is likely to be much smaller.

Meanwhile, Republicans say the rising number suggests the U.S. detention facility at Guantanamo Bay, Cuba, cannot be closed because that would mean either releasing hardened terrorists back into the fight or moving them into U.S. prisons, which many Americans oppose.

“Guantanamo remains the proper place for holding terrorists, especially those who may not be able to be detained as securely in a third country,” Senate Republican leader Mitch McConnell said Tuesday.

Although Obama said Tuesday that he still wants to close the detention facility, Defense Department press secretary Geoff Morrell suggested Wednesday that such plans were on hold. Congress has put severe limits on the endeavor.

Under significant political pressure, Obama has said he won’t release any more detainees to Yemen because of al-Qaida’s grip on that nation. Nearly half of the remaining 198 detainees at Guantanamo Bay are from Yemen.

U.S. officials believe two Saudis released from Guantanamo, one in 2006 and the other in 2007, may have played significant roles in al-Qaida activities in Yemen.

“We are right now left without either the money or the authority to move detainees from Guantanamo Bay,” Morrell said.

The Christmas Day attack on a jet arriving in Detroit has heightened concerns about Yemen because the suspect, a 23-year-old Nigerian passenger, claimed to be acting on instructions from al-Qaida operatives in Yemen.

Just days before the attempt to bring down the jetliner, the Obama administration sent six men held at the Guantanamo Bay detention center back to Yemen.

Republicans and an increasing number of Democrats in Congress had called on the administration to stop Guantanamo transfers to Yemen in light of the attack.

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Associated Press writer Pamela Hess contributed to this report.