Washington (CNN) -- A Pakistan-based terrorist group that is actively attacking American troops across the border in Afghanistan is an "arm" of the Pakistani intelligence agency, the top U.S. military officer told Congress on Thursday. The blunt accusation from the chairman of the Joint Chiefs of Staff, Adm. Michael Mullen, reflected the growing impatience of U.S. officials with Pakistan's unwillingness to stop the attacks and the belief that Pakistan is actively supporting the insurgents. But the recent high profile attacks by insurgents in Afghanistan represent a shift in strategy by the Taliban, who have ceded control of territory in much of the country, the U.S. secretary of defense said Thursday.

Mullen has spent a significant amount of time during his chairmanship building relations with the

OPTIONS:
- Afghanistan.
- American.
- CNN.
- Congress.
- Haqqani network.
- Joint Chiefs of Staff.
- Michael Mullen.
- Mullen.
- Pakistan.
- Pakistani.
- Panetta.
- Taliban.
- U.S..
- Washington.


Pakistan.