The Pentagon has said U.S. special operations troops launched a raid on January 8th in eastern Syria. Unnamed U.S. officials said the raid was carried out by the Expeditionary Task Force and was aimed at capturing top ISIS militants. Witnesses said the U.S. troops landed by helicopter and then left an hour and a half later carrying prisoners and bodies.

The raid took place near a remote village along the Euphrates River, according to the Syrian Observatory for Human Rights, a Britain-based watchdog organization, which reported 25 Islamic State group militants were killed.  No Americans were killed or injured during the operation, he said. Some Islamic State group fighters were killed.

Navy Capt. Jeff Davis, a Pentagon spokesman, described the raid conducted by the Joint Special Operations Command-controlled Expeditionary Targeting Force as “successful,” but he declined to provide specific information about the mission near Deir al-Zour in eastern Syria.

“It was focused on Islamic State group leadership,” Davis told reporters Monday at the Pentagon. “We don’t provide specific details on these types of operations.”  Davis said the mission was focused on gathering intelligence that could be used to inform future operations against the Islamic State group, such as the continuing assault on Mosul, the militants’ last urban stronghold in Iraq, and the future attack on Raqqa, its de facto capital in Syria.

A commander for the Syrian Democratic Forces said the attack targeted vehicles driven by senior IS militants coming from Raqqa, IS’s headquarters, and that the operation killed several militants from the group. Davis denied that prisoners were taken, saying there was “no detention from this operation”.

The unit, called the Expeditionary Targeting Force, is described as a group of about 200 Iraq-based commandos tasked with conducting raids, freeing hostages, gathering intelligence and capturing Islamic State leaders.

One raid in October 2015 in Iraq’s Kirkuk province freed dozens of hostages and resulted in the death of Master Sgt. Joshua Wheeler, a 39-year-old Delta Force operator who was the first American service member killed in a firefight with ISIS militants.  The father of four, who was thinking of retiring from the Army, became the first American in four years to die in combat in Iraq.  The 70 rescued hostages were about to be executed by Islamic State militants on the morning of the raid.

The US military has more than 5,000 troops on the ground in Iraq currently, a number that has steadily crept up since roughly 300 troops were deployed in June 2014 to secure the Baghdad airport.  In December, Defense Secretary Ashton B. Carter announced that the US would be sending 200 additional troops to Syria to help thousands of Kurdish and Arab fighters massing for an assault on the Islamic State’s stronghold of Raqqa.

Carter said the reinforcements would include American commandos and bomb-squad specialists. They will join the 300 Special Operations forces already working in eastern Syria to recruit, train and advise local Syrian militias to combat the Islamic State, also known as ISIL or ISIS.