Detainees liberated from the U.S. military prison at Guantánamo Bay, Cuba, have killed Americans, a senior Pentagon official told lawmakers.

The Department of Defense (DOD) official’s comments on Wednesday sparked criticism from Republicans opposed to closing the detention center in the wake of the deadly terrorist attack in Brussels and Paris claimed by the Islamic State (ISIS/ISIL), notes the Associated Press (AP).

“Paul Lewis, the Pentagon’s special envoy for Guantánamo detention closure, declined to provide the GOP-led House Foreign Affairs Committee with details,” reports AP. “He would not say whether the incidents occurred before or after President Barack Obama took office in January 2009.”

“What I can tell you is unfortunately there have been Americans that have died because of [Guantánamo] detainees,” said Lewis when questioned by Rep. Dana Rohrabacher (R-CA), adding, “When anybody dies, it is tragedy and we don’t want anybody to die because we transfer detainees.”

An Obama administration official told AP on condition of anonymity that Lewis was referring to an incident involving the release of an Afghan prisoner from Guantánamo while George W. Bush was president.

“During the Bush administration, 532 prisoners were released from Guantánamo, often in large groups to Afghanistan and Saudi Arabia – the two nationalities that made up the greatest number of prisoners,” points out AP.

“The Obama administration has released 144 detainees after a screening process that involves representatives from six government agencies and departments who must make an unanimous decision to release,” it adds.

Lewis testified before the House panel alongside Lee Wolosky, the State Department’s special envoy for shutting down Guantánamo.

Both Lewis and Wolosky reiterated President Barack Obama’s position that the prison is an effective propaganda tool for ISIS and keeping it running negatively impacts U.S. national security.

A bipartisan group of lawmakers has repeatedly prevented Obama from closing down the detention center. Legislation approved by members of both parties and signed into law by President Obama prohibits the transfer of Guantánamo detainees to prisons on U.S. soil.

Nevertheless, the Obama administration submitted a proposal to Congress in February for shutting down the facility.

The State Department’s Wolosky argued that the detention center failed to prevent Tuesday’s attacks in Brussels that killed at least 34 people and injured more than 200 or the deadly November 13 attacks in Paris.

“There are unfortunately going to be acts of terrorism, probably whether the facility is opened or closed,” Wolosky said. “The proper analysis is, ‘What are the risks of keeping it open in light of the very obvious use of that facility as a propaganda tool,’ which, frankly, you should not have to question.”

The AP reports:

The committee’s hearing marked the first open exchange between the Obama administration and Congress over the utility and future of the prison since Obama sent his plan for shutting it down to Capitol Hill last month. The proposal was greeted with firm opposition from Republicans, who declared his proposal to deliver an unfulfilled campaign promise a non-starter.

Currently, the Guantánamo prison is housing 91 men, down from an estimated 250 when Obama took office.

Earlier this month, the Director of National Intelligence (DNI) revealed that five percent of Guantánamo prisoners released since January 2009, when the President Obama launched a multi-agency screening process, have returned to terrorist activities and eight percent are suspected of it.

“That compares to 21 percent confirmed and 14 percent suspected under the earlier system,” notes the AP.