A razor wire-topped fence and watchtower at the abandoned Camp X-Ray detention facility at Guantanamo Bay. Mladen Antonov/Agence France-Presse via Getty Images)

A senior Pentagon official said Wednesday that the release of detainees from the U.S. military’s prison at Guantanamo Bay, Cuba, has led to American deaths, though he did not provide any specific examples.

Paul Lewis, the Defense Department’s special envoy for Guantanamo closure, told the House Foreign Affairs Committee under questioning that “unfortunately, there have been Americans that have died because of Gitmo detainees.” He did not provide any details on whether those deaths occurred in terrorist attacks or on a military battlefield, or how many Americans were killed.

“Sir, when anybody dies, it’s a tragedy and we don’t want anybody to die because we transfer detainees,” Lewis told Rep. Dana Rohrabacher (R.-Calif.) when pressed on the issue. “However, it’s the best judgment and the considered judgment of this administration and the previous administration that … we should close Gitmo.”

U.S. officials have said previously that detainees were involved in some operations that killed Americans, including the 2011 attacks in Benghazi, Libya. But Lewis’s comments Wednesday led to new calls to keep the prison open and keep its most hardened detainees there.

Closing the military prison at Guantanamo was a campaign promise of President Obama’s, and it has remained a point of contention throughout his time in the White House. Ninety-one detainees remain at the facility, with Obama having transferred out about 144, while President George W. Bush released 532 during his administration, according to U.S. officials.

The Office of the Director of National Intelligence (DNI) said this month in its most recent report on former Guantanamo detainees that of the 532 detainees released by Bush, 111 of them are confirmed to have returned to terrorist activities. Twenty-nine of those are dead, 25 are back in custody and 57 remain free. An additional 74 of the 532 detainees are suspected of returning to the battlefield.

Of the 144 detainees Obama has released, seven are confirmed to have returned to militant activities and 12 are suspected of having done so, according to DNI officials. Overall, about 30 percent are believed to have done so.

Sen. Tim Scott (R-S.C.) said in statement Wednesday that Lewis’s comments “are a clear admission” by the Obama administration that attempts to close the detention center entirely are detrimental to natural security.

“The President must rescind his Guantanamo plans, and instead begin detaining captured ISIS fighters at the facility,” Scott said, using an acronym for the militant group. “This is bigger than politics, and the President must stop putting campaign promises first and American lives second.”

Rep. Eliot Engel (D-N.Y.) and Lee Wolosky, a State Department special envoy for Guantanamo closure, both pointed out during the hearing Wednesday that the United States has also effectively prosecuted and imprisoned numerous terrorists in the continental United States.