The U.S. military says it conducted four counterterrorism strikes against al-Qaeda militants in Yemen in recent months, including one on May 19 that killed four enemy combatants, the Associated Press reports.

U.S. Central Command says the strikes killed a total of 15 members of al-Qaeda in the Arabian Peninsula. The four strikes were not previously announced.

Altogether, the U.S. has launched nine strikes this year against the group, which the U.S. says is a persistent threat in the region and to Western interests.

The Pentagon has been increasing its military support for operations against AQAP militants in Yemen, including intelligence, ships and special operations forces. American special operations forces have been advising the Yemeni, Emirati and Arab coalition forces in the region.

Al-Qaida had gained ground amid the chaos in Yemen, AP says.