Libya has seen an influx of Islamic State extremists in recent months, while the number of jihadists in Iraq and Syria has dropped by several thousand, a US defense official said Thursday.

About 5,000 IS fighters are now in Libya, the official said, up from earlier estimates of between 2,000 and 3,000.

The official added the United States now believes there to be between 19,000 and 25,000 IS fighters in Iraq and Syria, down from a previous tally of between 20,000 to 33,000.