The commander of the U.S.-led coalition against the Islamic State group says there's an urgent need to encircle the extremists' stronghold in the Syrian city of Raqqa because of intelligence warnings that attacks on Western targets are being plotted there.

Army Lt. Gen. Stephen Townsend spoke to reporters at the Pentagon on Wednesday from his headquarters in Baghdad.

Townsend said the coalition is using airpower to strike available targets around Raqqa, as a first step to spoil the plotting. But it needs to more fully isolate the city soon, he said, to increase the pressure. That will be followed by an assault on the city led by Arab and other local fighters, he said.

Townsend said it's unclear when and where in the West the extremists intend to strike.