More than 500 Pakistanis --among them suspected militants as well as many civilians --have so far been killed in the attacks by the US drones.

A US drone has fired a missile into a base of Pakistani Taliban leader Baitullah Mehsud in northwest Pakistan, killing at least three people.

"We have received reports of a drone attack near Makeen and we are checking how many people were killed or wounded," a Pakistani military official said Tuesday, referring to an area in the South Waziristan near the Afghan border where Tehrik-i-Taliban's leader Baitullah Mehsud is based.

"A missile attack by a suspected US drone took place in rugged mountainous terrain in Neej Narai," said another Pakistani security official wanted not to be named.

Neej Narai, 60 kilometers northeast of Wana, the main town in South Waziristan, is known as a stronghold of Pakistan Taliban chief Baitullah Mehsud.

Although the US military maintains a silence policy on drone attacks; it is believed to be the only operating force in Afghanistan that conducts drone attacks in the region.

At least 500 Pakistanis -- suspected militants as well as many civilians -- have been killed in the drone attacks.