Troops secured footholds Wednesday in a Pakistani valley overrun by the Taliban, killing 11 enemy fighters and discovering five headless corpses near the region's main town, the army said.

Elsewhere in the turbulent northwest, police said dozens of assailants stormed a transport depot handling supplies for NATO troops in neighboring Afghanistan and torched eight trucks before escaping.

Rising violence, including a string of attacks on NATO and U.S. supplies, have fed concern that more of Pakistan's border region is slipping from government control and into the hands of the Taliban and Al Qaeda.

Afghan President Hamid Karzai warned Wednesday that the threat militants pose to both countries is very real.

"Terrorists and extremists are extending their reach in whole areas of our countries," Karzai told a regional economic conference in the Pakistani capital, Islamabad.

Under strong U.S. pressure, Pakistani authorities abandoned peace talks last month with Taliban militants and launched a military operation to expel them from their stronghold in the Swat Valley.

The army claims to have killed more than 750 militants since the operation began. But the fighting has also driven some 800,000 people from their homes, creating a humanitarian emergency that could undercut support for the pro-Western government.

The army said Wednesday that commandos airlifted into the valley the day before had established a "firm hold" in the remote Piochar area, the rear base of Swat Taliban leader Maulana Fazlullah.

Troops were also consolidating their positions near a strategic bridge and a shrine in the valley, an army statement said. Various clashes in the previous 24 hours left four soldiers and 11 militants dead, it said.

The five headless bodies were found near the valley's main town, Mingora, the army said, giving no details of the victims' identities. Residents have said the Taliban have repeatedly decapitated opponents and dumped their bodies in Mingora.

The army has yet to start operations in Mingora, where witnesses say Taliban insurgents are in control and preparing for what could be bloody door-to-door fighting.

The army says it is proceeding carefully, wary that civilian casualties and massive disruption could sap public support for a sustained operation to undo recent Taliban gains.

It says it has no information to corroborate accounts from refugees of dozens of people killed and injured in the fighting, which has included massive airstrikes on militant targets.

Tens of thousands of refugees have found refuge in camps run by the government and the United Nations. Others are living with relatives and friends.

Lawmakers have raised concern about those so far unable to escape the valley, in part because of a curfew imposed by the army.

Syed Allahuddin, a lawmaker from Swat who represents the main ruling party, said some 700,000 people were stranded in the valley with dwindling supplies of food and water.

"People are facing grave trouble because they couldn't get the foodstuffs to provide for themselves and their children," Allahuddin said.