The U.S. military's top officer is accusing Pakistan of supporting attacks on U.S. targets in Afghanistan.

Joint chiefs of staff chairman Admiral Mike Mullen told a U.S. Senate hearing the al-Qaida-linked Haqqani network, acting with support from Pakistan's military spy agency ISI, planned and conducted the assault last week on the U.S. Embassy in Kabul.

He said the ISI also supported the truck-bomb attack by Haqqani insurgents on a NATO base in central Afghan province of Wardak on September 10 that wounded 77 U.S. soldiers.

Mullen said Pakistan's Inter-Services Intelligence uses the Haqqani network as a “veritable arm” to act in Afghanistan against Afghan and coalition forces and expressed concern about the impunity with which extremist groups are allowed to operate from Pakistan.

Admiral Mullen said that by exporting violence, Pakistan has eroded its internal security and international credibility, and threatened its economic well-being. But he added that he believes that the United States should remain engaged with Islamabad.

U.S. Defense Secretary Leon Panetta told the hearing “we cannot allow terrorists to save safe havens from which they launch attacks and kill U.S. forces.”

Islamabad rejects U.S. accusations and says it is cooperating in the battle against militants in the region.

Pakistan's Information Minister Firdous Ashiq Awan told VOA that Pakistan is working for peace in Afghanistan, and that what she called “propaganda” accusing Pakistan of helping militants is meant to sabotage Islamabad's efforts.

Separately, Pakistani Interior Minister Rehman Malik promised to take action against the Haqqani network if the United States provides sufficient intelligence to help in the effort.