Reports of US forces carrying out operations inside Pakistan have drawn strong protests from Pakistani leaders.

Asif Ali Zardari, the Pakistani president, told NBC news that the US was forbidden from allowing any operations without permission.

"If the American troops are coming in without letting us know, without the Pakistani permission, they are violating the United Nations charter."

Series of raids

US commandos crossed the border into Pakistan on September 3 to attack a suspected al-Qaeda target that officials said was contributing to violence in Afghanistan.

Five people were killed when unmanned drones fired missiles into a village in South Waziristan last Wednesday evening, according to Pakistani officials.

And also last week, Pakistani troops were reported to have fired in the air to repel a US ground incursion into South Waziristan.

But there has been frustration in Washington over Pakistan's apparent slowness to act against fighters on its territory.

US officials say that armed fighters are using the tribal areas in northwestern Pakistan as a base to launch attacks on Afghan and US forces operating across the border.