NATO officials say insurgents who carried out Sunday's deadly assault on a remote NATO outpost in eastern Afghanistan were able to penetrate the base before they were driven away by U.S. air strikes.  Nine American soldiers were killed in the assault.  Fifteen other U.S. troops and four Afghan soldiers were wounded.  From Islamabad, VOA's Barry Newhouse has more on one of the single deadliest attacks for U.S. forces since the 2001 invasion.

The attack began early Sunday at a NATO outpost built just last week in Kunar, a province in eastern Afghanistan that borders Pakistan.

NATO officials said a large group of insurgents had secretly moved into a nearby village, where they launched a complex assault that lasted for much of the day.

NATO spokesman Mark Laity told reporters in Kabul that while insurgents regularly attack combat outposts, Sunday's assault was larger than normal and insurgents managed to fight their way inside fortified walls.

"They attempted to break into that base.  They did make some penetration.  But over all they were repelled and they took very heavy casualties themselves," Laity said.  "And then we brought in air power to stabilize the situation in a fight that then lasted for several hours."

It was unclear how many insurgents were involved in the fighting, but the NATO spokesman said airstrikes inflicted heavy casualties after the fighters were repelled at the outpost.

It is also unclear where the insurgents came from or what group they belong to.

Several Afghan Taliban groups operate in the east of the country and U.S. and Afghan officials say Pakistani Taliban fighters also regularly attack NATO troops near the border.  The fighting has led to a spike in NATO troop deaths and criticism that Pakistan is not doing enough to crack down on Taliban havens in its tribal regions.

Senior Pakistani officials counter that Afghan officials have been unwilling to work more closely on controlling their shared 2500 kilometer border. They also say Afghan and coalition forces can do more to stop militants from crossing into Pakistan.

The increased tension over militant safe havens has led several Pakistani officials to express worry that the United States is considering unilateral military action against fighters in the tribal regions. In recent days Pakistani officials from across the political spectrum have insisted foreign troops will not be allowed to operate in Pakistani territory.  

Senator Mushahid Hussain, the chairman of Pakistan's Senate Foreign Relations Committee, said resolving the situation should be done through dialogue - not force.

"The use of force is counter productive. We must engage people in discussions and we welcome negotiations with those who are willing to lay down their arms," he said.

Despite favoring talks, senior Pakistani leaders say they are aware how serious the situation in the tribal regions has become. On Monday, Prime Minister Yousuf Raza Gilani said he understands concerns that the tribal areas could be used by foreign militants to plan international terrorist attacks.