The Pentagon said Friday it played no part in an unusual deal between the PKK's Syrian offshoot, the People's Protection Units (YPG) and Daesh.

The U.S.-backed YPG had independently cut a deal with the Daesh that let a group of about 70 terrorists leave Tabqa, an important city by a dam near the terror group stronghold of Raqqa.

But as soon as they left the city, U.S. aircraft tracked and killed several of them, officials said.

"This was an agreement for them to leave the Tabqa dam and to leave the remaining portions of the city that Daesh held," Pentagon spokesman Jeff Davis said.

"It doesn't change the fact that when we see Daesh fighters on the battlefield and have a clean shot at them, we will continue to take it," Davis added.

He stressed that they were not considered to have surrendered.

According to a U.S. official, the YPG deal had been in the works for a couple of weeks.

The U.S. knew about it, but "it wouldn't have been our preference," the official told reporters.

The YPG allowed the fighters to leave in return for dismantling bombs surrounding the dam, surrendering their heavy weapons and quitting Tabqa city.

Nothing about that precluded the Daesh members from being pursued, Maj. Adrian Rankine-Galloway said.

"This is combat. They didn't make a deal with us," he said.

The U.S. official said America always observes the laws of armed conflict and Geneva Conventions, meaning an unarmed Daesh member waving a white flag would not be targeted.

Davis said a dam-assessment team was headed to the structure to make sure it had not been damaged by Daesh, although so far there had been no issues detected.