The Pentagon transferred the head of the Islamic State terror group's chemical weapons development unit to the Iraqi government Thursday shortly after the U.S. captured him in a raid, Pentagon press secretary Peter Cook announced.

Cook stressed the U.S. would keep ISIS detainees only for the "short term," handled on a "case by case" basis. "We have a government on the ground in Iraq, a partner in the fight against ISIL, that we feel confident we can rely on in this instance."

A defense official who would not reveal his identity reached by Fox News after the briefing confirmed the Pentagon has no plan on handling ISIS detainees. Cook would not say whether the U.S. government had access to ISIS detainees once turned over to the Iraqi government. Many GOP lawmakers have urged the Pentagon to send the detainees to Guantanamo Bay, which President Obama has vowed to close.

A GOP congressional aide told Fox News, "The law requires a comprehensive detainee policy. By definition, 'we'll figure it out if we ever capture anyone' is not a comprehensive policy."

U.S. special forces captured Sulayman Dawud al-Bakkar, also known as Sleiman Daoud al-Afari, in a raid last month in northern Iraq, according to Iraqi and U.S. officials. The special commando unit was deployed to Iraq to conduct raids and collect intelligence on the ground. 

The Pentagon press secretary said al-Bakkar's capture and transfer could be "a template for future cases."

Cook said the airstrikes conducted as a result of al-Bakkar's capture "disrupted and degraded" the group's chemical weapons capabilities, but did not necessarily eliminate the problem.

"We feel good about the damage we've done to the program," he said.

Cook declined to provide details of the strikes but said the information they've received will allow the U.S. to conduct additional strikes.

Al-Bakkar worked for the late President Saddam Hussein's now-dissolved Military Industrialization Authority, where he specialized in chemical and biological weapons. Iraqi intelligence officials said he is about 50 years old and headed the Islamic State group's recently established branch for the research and development of chemical weapons.

He was captured in a raid near the northern Iraqi town of Tal Afar, the officials said. They spoke on condition of anonymity because they weren't authorized to discuss the matter publicly.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.