WASHINGTON: Insurgent attacks have put US and NATO forces on the defensive in eastern Afghanistan, an area recently touted as a counter-insurgency success but now a focus of spreading insecurity, analysts say.

In the latest attack, at least nine US soldiers were killed Sunday when insurgents stormed a remote combat outpost in Kunar province near Pakistan.

It was the deadliest attack against US forces since 2005, but it followed a trend of bolder and more capable insurgent operations as Pakistan's new government has taken a hands-off approach to militant sanctuaries in its tribal areas.

"It's very serious because NATO is already under a lot of pressure," said Bruce Riedel, a former CIA officer now at the Brookings Institution.

"There used to be one deteriorating front, the front in the south. Now that we see the situation in the east is heating up too, it really stretches NATO and American resources very far," he said.

Increasingly concerned about the rising violence, the Pentagon has begun shifting the weight of its combat operations to Afghanistan but within constraints on available forces imposed by the war in Iraq.

It has repositioned an aircraft carrier from the Gulf to the Arabian Sea to support military operations in Afghanistan, extended the deployment of 2,200 Marines in the south and is weighing deeper troop cuts in Iraq to free up more soldiers.

Currently there are 36,000 US troops in Afghanistan, and 150,000 in Iraq, the Pentagon said.

Admiral Michael Mullen, the chairman of the Joint Chiefs of Staff, meanwhile made an unannounced visit to Islamabad over the weekend to urge the Pakistan military to do more to stem the flow of insurgents into Afghanistan.

"Part of the effort here is not just militarily in Afghanistan, but it's working with our Pakistan colleagues, and the Pakistani government in addressing the situation on the Pakistan side of the border," said Bryan Whitman, a Pentagon spokesman.

But Pakistan has shown little willingness to get tough on insurgents.

On Monday, Afghanistan's President Hamid Karzai directly accused the Pakistani intelligence services of fomenting the violence, charges that some experts regard as credible.

"It shows that there is a real breakdown in trying to build a common front between Afghanistan, Pakistan and India against the Islamic extremists. And that is not good news," said Riedel.

Sam Brannen, an expert at the Center for Strategic and International Studies, said the ability of US and NATO forces "to impact events and to really know what is going on ends at the Pakistani border," said

"It is a 2,400 kilometre border. It is very difficult to defend in the best of times, but these are not the best of times," he said.

The sense that the war is shifting in the Taliban's favour in the east also undermines support for NATO forces in the area, he said.

"The tribes in that region are notorious for shifting allegiances. And the winning party, whoever is on top, enjoys their support," he said.

"I think you're seeing a growth in the number of recruits of young men who are joining up for the jihad. So the tables are turning just when Pakistan is taking more of a laissez-faire approach to that area again," he said.

US military officials have noted that not only is the incidence of attacks up but they have grown more sophisticated.

Hundreds of militants were reported to have taken part in Sunday's assault, an hours-long engagement that officials described as fierce and well-organised.

Last month, Taliban insurgents succeeded in blasting open a prison in the southern city of Kandahar and freeing hundreds of captured insurgents.

Analysts see further evidence of the Taliban's expanded reach in the July 7 suicide bombing at the Indian embassy in Kabul, which killed as many as 60 people, and the attempted assassination of President Hamid Karzai at a military parade in April.

"We've definitely seen the Taliban learn from its mistakes, and employ tactics which are much more similar to the tactics we've seen Iraqi insurgents using," said Riedel.

"And there is good reason to believe that is not an accident, that al-Qaeda is providing the link between insurgent tactics in Iraq and insurgent tactics in Afghanistan," he added.