The U.S. military's top officer has accused Pakistan of exporting violent extremism to Afghanistan by using militants as a “veritable arm” of its military spy service.

The chairman of the Joint Chiefs of Staff, Navy Admiral Mike Mullen, told U.S. senators Thursday that Pakistan's Inter-Services Intelligence uses the al-Qaida-linked Haqqani network to act in Afghanistan against Afghan and coalition forces.

Admiral Mullen said that by exporting violence, Pakistan has eroded its internal security and position in the region. He also said Pakistan has undermined its international credibility and threatened its economic well-being.

Speaking alongside Mullen in Washington, U.S. Defense Secretary Leon Panetta says Pakistan must take steps to prevent safe havens for the Haqqani network. Late last week, Panetta warned the United States would take action to protect its forces in Afghanistan from Pakistani-based militants, but he did not elaborate.

U.S. officials maintain that Haqqani militants have been attacking Afghan and coalition troops in Afghanistan and taking shelter in sanctuaries across the border in Pakistan's North Waziristan tribal region.

Pakistan has repeatedly rejected such accusations by the United States. 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.

Malik told reporters Wednesday that Pakistan is cooperating with the United States in tackling the issue of militancy in the region. But he maintained that the Haqqani network is not in Pakistan.

Washington blames Haqqani operatives acting with ISI support of planning and conducting a September 11 truck bomb attack, as well as last week's assault on the U.S. Embassy in Kabul. Admiral Mullen also says the United States has credible intelligence that the Haqqanis were responsible for a June 28 attack against the Inter-Continental Hotel in the Afghan capital, which is popular among foreigners and government officials.