WASHINGTON, D.C. — The number of Islamic State (ISIS/ISIL) jihadists in Libya who aspire to attack Europe or the United States has more than doubled to between 4,000 and 6,000 in the last 12 to 18 months, but militias there have managed to limit the terrorist group’s growth, says the commander of U.S. forces in Africa.

On Thursday, Gen. David Rodriguez, head of U.S. Africa Command, told Pentagon reporters that ISIS’ stronghold in Libya is in the port city of Sirte, only a few hundred miles across the Mediterranean Sea from the shores of Europe.

The commander told reporters:

In north Africa, the big threat there revolves around Libya and the growing threat of ISIS in the region, and we work with many, many partners there to help that situation out, from the European Union, who has a strong mission in the Mediterranean Sea to mitigate the challenges of migration, to Tunisia, where we’re continuing to build some significant partner capacity, as well as in Niger and Chad, who also have challenging borders in the area.

Asked about the number of ISIS fighters in Libya, Gen. Rodriguez responded that the U.S. intelligence community estimates there are “around 4 to 6,000.”

“It is probably about doubled in the last 12 to 18 months based on what their assessments were last year,” he continued.

The general noted that Libyan militias have limited ISIS’ expansion in the country.

“They’ve had activities that have limited the growth and the challenges that are out there,” he told reporters.

“So you know, it’s uneven and it’s not you know consistent across the board… But they are contesting the growth of ISIS in several areas across not Libya, not all,” added Rodriguez.

The commander minimized the possibility that ISIS could conquer large swathes of territory as it has done in Iraq and Syria.

“They don’t have the homegrown people that know as much about Libya like they did in Iraq and Syria,” he said. “So it’s different conditions. So [the] Libyan people are also, you know, different in that the way they treat and respond to foreigners.”

“The majority on the Libyan militias, first of all, they can fight. They’ve been fighting for a long time… they don’t like, you know, external influences like that there,” added the U.S. general.

Western governments, worried that ISIS will take advantage of the political and security chaos in Libya to mirror its success in seizing land in Iraq and Syria have expressed concern about the terrorist group’s growth in the Northern African nation, reports Voice of America (VOA).

“Since 2014, loose coalitions of armed brigades have backed rival governments in Tripoli and the east,” adds the report. “Western governments back the Government of National Accord, in part as the best chance for uniting armed factions against Islamic State.”

The general stressed that the limited U.S. airstrikes in Libya have focused on targets “that pose an imminent threat to U.S. interests and personnel.”