Washington: Pakistan-based Haqqani network, blamed for this week's attack on the American Embassy in Kabul, is one of Afghanistan's most dreaded and sophisticated insurgent groups that have the backing of elements within the Pakistani security establishment, according to a report.

Although the Haqqani network is officially subsumed under the larger Afghan Taliban umbrella group led by Mullah Omar and his Quetta Shura, the Haqqanis maintain distinct command and control, and lines of operations, according to key findings by the Institute for the Study of War, a Washington-based independent think-tank.

Siraj Haqqani, the son of the famous anti-Soviet fighter Jalaluddin Haqqani, is the current leader of the Haqqani network. Siraj is more extreme than his father and maintains closer ties to al-Qaeda and other foreign extremists in
Pakistan, the report had said.

The group maintains a safe haven in North Waziristan in Pakistan and across Afghanistan's southeastern border. The Pakistani Army has consistently refused to launch a military operation in North Waziristan despite the presence of al-Qaeda senior leadership, the report said.

"Elements within the Pakistani security establishment continue to view the Haqqani network as a useful ally and proxy force to represent their interests in Afghanistan. To this end, Haqqani forces have repeatedly targeted Indian infrastructure and construction projects in Afghanistan," said the report which was released last year.

The most explicit comment to link the Haqqani network and Pakistani establishment came yesterday when America's top diplomat to Islamabad Cameron Munter said the US has evidence linking the Pakistan government to the terror network, which was behind the attack on the American Embassy in Kabul.

"Let me tell you that the attack that took place in Kabul a few days ago, that was the work of the Haqqani network.

"And the facts, that we have said in the past, that there are problems, there is evidence linking the Haqqani network to the Pakistan government," he said.

The network was able to expand beyond Loya-Paktia towards Kabul from 2005 to 2006, providing the network with the ability to execute attacks in the Afghan capital, the report said.

From 2008 to 2009, the network launched an offensive aimed at strengthening their positions in Loya-Paktia, while projecting suicide bombers into Kabul to launch some of the most lethal attacks of any insurgent group in Afghanistan.

Until recently, US and coalition troops lacked sufficient forces to reverse the momentum of the Haqqani network. But an increased drone campaign by the US against senior Haqqani safe havens in North Waziristan has disrupted the network's ability to plan and execute operations.

Despite recent progress, Haqqani network operations can regenerate if not continually pressured, the report warned.