ISIS is planning additional "significant" external operations against the West from its de-facto capital in Raqqa, Syria, the top U.S. commander in Iraq told reporters Wednesday.

“I will say that we actually aren't sure how pressing it is, and that's what's worrying us,” Lt. Gen. Stephen Townsend said via teleconference from Baghdad. “We know they're up to something. And it's an external plot, we don't know exactly where, we don't know exactly when.”

Townsend said it was important to surround Raqqa quickly to cut off ISIS because of the growing terrorist threat to the West.

PENTAGON: COALITION LAYING GROUNDWORK TO RETAKE RAQQA

Townsend would not reveal any more about the threat, but said some links include plots against the United States, France and other European countries.

Despite these threats, Townsend said there was no plan to accelerate the timeline to retake Raqqa from ISIS. It will take longer than the current operation to retake Mosul, Townsend admitted. 

He said ISIS fighters are still moving in and out of Mosul because the city is not completely surrounded by Iraqi or Kurdish forces. In the past week, a small number of ISIS fighters and their family members left Mosul, he told reporters.

IRAQI FORCES EVACUATE 1,000 CIVILIANS NEAR MOSUL

“We don’t have a complete encirclement of Mosul,” Townsend said.

Townsend said ISIS ramped up its use of family members, including women and children, as cover to move around the battlefield, after U.S. jets killed hundreds of ISIS fighters months ago.

The spike in U.S.-led airstrikes supporting the Mosul operation means there will be fewer airstrikes in Syria because the Iraqi-led Mosul operation is the “main effort,” Townsend said. “Other efforts will get by with some less,” he admitted.  

The composition of the force to capture Raqqa remains a source of contention in the region. Turkey does not want Syrian Kurds included in the battle.

Townsend says the Kurdish YPG militia would be included in such an operation “soon” but would not be more specific citing operational security about an upcoming mission.

The Turkish government has objected to U.S.-backed Kurdish fighters taking part in the Raqqa operation, despite proving to be the best ground force against ISIS in Syria, officials say. The U.S.-backed Kurds defeated ISIS in the battle for Kobani in 2014, a Syrian village on Turkey’s border, the first major victory against ISIS.

Despite Turkish objections, Townsend said, “The only force that is capable in the near-term is the Syrian Democratic Forces, of which the YPG are a significant portion.” Townsend said negotiations with Turkey were underway to resolve the issue.  

Townsend said the assault force to take back Raqqa would be a “light footprint” comprised of local forces from Raqqa and the surrounding area. Arab fighters will be a part of the force, which would be trained outside of Raqqa in northern Syria, he added.

Further complicating the battlefield, Townsend said there are fighters aligned with the Kurdish Worker’s Party, better known as the PKK, fighting ISIS in Sinjar in northern Iraq to protect the Yazidis. The State Department considers the PKK a terrorist group because of its decades long insurgency in Turkey killing thousands. 

Lucas Tomlinson is the Pentagon and State Department producer for Fox News Channel. You can follow him on Twitter: @LucasFoxNews