WASHINGTON - The United States has accused Pakistan's intelligence agency of using the Haqqani Network to wage a "proxy war", hardening its criticism of Islamabad's ties with Taliban-allied factions fighting NATO and Afghan troops in Afghanistan.

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, said that in a discussion with Pakistan's army chief that lasted about four hours, he had pressed Pakistan to break its links with the militant group.

"We covered ... the need for the Haqqani Network to disengage, specifically the need for the ISI(Inter-Services Intelligence） to disconnect from Haqqani and from this proxy war that they're fighting," he said in a speech to the Carnegie Endowment for International Peace on Tuesday.

"The ISI has been doing this - working for - supporting proxies for an extended period of time. It is a strategy in the country and I think that strategic approach has to shift in the future."  

Washington blames the Haqqani Network, one of the most feared Taliban-linked groups fighting in Afghanistan, for last week's attack on the US embassy and other targets in Kabul.

It has in the past suggested that Pakistan's powerful Directorate of Inter-Services Intelligence (ISI) maintains ties to the network to guarantee itself a stake in any political settlement in Afghanistan when American troops withdraw.

Accusing the ISI of using the Haqqanis to wage a "proxy war" goes further, and risks fuelling tension between Islamabad and Washington, which have been running high since al Qaeda leader Osama bin Laden was killed in a surprise US Navy SEALs raid in Pakistan in May.

"In the past, they have been saying that Pakistan is looking the other way with the Haqqanis, but this term - using them as proxies for Pakistani interests - that is something new," said Rahimullah Yusufzai, editor of the Peshawar edition of the News daily and an expert on Afghanistan.

The Haqqani network is perhaps the most divisive issue between Pakistan and the United States. Washington has repeatedly pressed Pakistan to go after the network, which it believes enjoys sanctuaries in Pakistan's unruly ethnic Pashtun tribal region of North Waziristan on the Afghan border.

Pakistan denies accusations it has ties to the Haqqanis.