Story highlights Strikes target what's known as the Khorasan Group, officials say

It is too early to have an assessment of the results

Khorasan is a group of hard-core al Qaeda operatives

U.S. aircraft have concluded a third round of strikes against an al Qaeda cell inside Syria, two U.S. officials with direct knowledge of the just-completed mission told CNN on Thursday.

The officials said it was a small number of strikes and that the targets included at least one top operative of what's known as the Khorasan Group. The sources would not say who was targeted. They said it is too early to have an assessment of the strikes' results.

Khorasan is a group of hard-core al Qaeda operatives, many of whom moved to Syria from Pakistan in the last few years.

The U.S. government has expressed concern about the group's ability to make bombs that can get past security screening in airports and elsewhere. It targeted the Khorasan Group with a series of strikes in Syria in September.

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Those attacks came amid intelligence that suggested the group was plotting against a target in the U.S. homeland, as well as other Western targets, a senior U.S. official told CNN at the time.

The group has "suffered" setbacks as a result of the strikes, which have killed a number of fighters and forced it to spread out, one law enforcement official who has seen the intelligence assessments said Thursday.

Another U.S. official said "some have been killed. They're being hunted down and they have to think about what they do and that's disruptive."

At the same time, some of the Khorasan leadership is still believed to be alive and the group continues to pose a threat, according to the officials, who say some are still in Syria, actively plotting against the United States.