CIA Director John Brennan warned that ISIS still has a large fighting force and is sending operatives to launch attacks in the West. 

Chief intelligence correspondent Catherine Herridge reported this morning on Brennan's rare public testimony to Senate lawmakers.

Brennan said ISIS is likely to use more "guerilla tactics" and launch attacks outside the Middle East, including in the U.S., to compensate for a loss of territory in Iraq and Syria. 

He said that despite battlefield setbacks, ISIS's ability to carry out global attacks - as it did in Paris and Brussels - has not diminished. 

And he warned that ISIS is using "refugee streams, traditional smuggling routes and legitimate travel" to move its operatives into place.

Herridge noted that Brennan laid out "sobering statistics" on the increase in ISIS followers in the Sinai and North and West Africa, which has now reached 15,000 outside of Iraq and Syria.

Watch the report above.

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