A U.S. defense official says new intelligence assessments show the number of Islamic State fighters has dropped in Iraq and Syria, but is rising in Libya.

The official says reports suggest there are 19,000-25,000 IS fighters in Iraq and Syria, compared to an earlier range of 20,000 to more than 30,000.

The decrease may explain some of the increase of IS in Libya, which has risen from a couple thousand to about 5,000.

The official says coalition airstrikes and military operations in Iraq and Syria have killed IS fighters and made it more difficult for them to move into the region or recruit others. As a result, some may be going into Libya.

The official was not authorized to discuss the numbers publicly and spoke on condition of anonymity.