A series of drone raids have been carried out this month in North Waziristan, home to fighters loyal to the Taliban, al-Qaeda and the Haqqani network.
A number of US raids in early January are reported to have targeted Hakimullah Mehsud, the leader of the Pakistani Taliban.
He was initially reported dead, but an audio recording purportedly carrying a message from Mehsud dispelled rumours of his death and vowed revenge for the drone programme.
The US never confirms drone attacks, but its forces in neighbouring Afghanistan and the Central Intelligence Agency are the only ones known to use the unmanned aircraft capable of firing missiles.
The attacks have often resulted in civilian deaths, stirring anger among Pakistanis and even bolstering support for the Taliban and anti-US sentiment.
Toll of innocents
Washington's refusal to comment on its alleged attacks has been criticised, with even supporters of the raids as a tool in Washington's fight against the Taliban saying that the US needs to be more open to counter the fighters' allegations that only innocent civilians are dying.
"The US government doesn't even suggest what the proportion of innocent people to legitimate targets is,'' Michael Walzer, an American scholar on the ethics of warfare, said.
"It's a moral mistake, but it's a PR mistake as well.''
According to the statistics compiled by Pakistani authorities, drones killed 708 people in 44 attacks targeting the tribal areas in 2009. Authorities said more than 90 per cent of those killed in the raids were civilians.