Jeffrey said in a statement of the US State Department that the United States does not know the rank of Daesh commander Abu Bakr al-Baghdadi.
He added, "Daesh has lost its last stronghold in Syria at the beginning of the week and that was a "great day," pointing out that the war against Daesh will continue and the US troops will stay in Syria in specific number just for help.
"This is not the end of the fighting against Daesh. This will continue, but in a different way of fighting," Jeffrey told the journalists.
"The Coalition's focus was on the permanent defeat of Daesh and to put pressure on the governments to return the foreign fighters who have been captured during the conflict," Jeffrey said.
"Most of the prisoners detained by the Syrian Democratic Forces were Iraqis and Syrians. They would be sent back to their communities to eliminate extremism, reintegrate them and in some cases to punish them," he said.
Reports have denied that the US-led Coalition is considering to set up an international tribunal to try the prisoners. "We are not looking at this at the moment," he said.
He said that it was difficult to estimate a number of prisoners, including Iraqis, Syrians and foreign elements detained by SDF. "People talk to me and say they are at the level of 7,000 or more, but maybe the number has increased over the weekend," he said.
Just before the final attack on al-Baguz at the weekend, the Syrian Democratic Forces said it had 800 IS' foreign elements and over 2,000 wives and children of IS' elements.
On Monday, the Democratic Autonomous Administration called for the formation of an international court to try IS' mercenaries who were captured by SDF.