The US state department on Wednesday authorised a reward of up to $5m for information leading to the location, arrest, or conviction of Mehsud.
The state department website said Mehsud posed a threat to US troops in Afghanistan and has facilitated cross-border attacks from Pakistan.
Mehsud is believed to be in the tribal areas of South Waziristan.
Meanwhile, in the adjoining region of North Waziristan, intelligence officials said four people were killed after a suspected US drone aircraft fired two missiles into a house outside the town of Mir Ali.
"Two missiles fired from a suspected US drone hit the compound of a local pro-militant tribal elder Malik Gulab Khan, killing four residents," a local security official told the AFP news agency.
Other Pakistani officials, however, denied there had been an attack.
"There was no missile strike," said Habibullah Khan, an administration official in the Federally Administered Tribal Areas, of which North Waziristan is a part.
Residents of Mir Ali said they had heard an explosion in a house, but they had no details about possible casualties.
A missile believed to have been launched by an unmanned US drone killed at least seven suspected pro-Taliban fighters in South Waziristan on Wednesday, intelligence officials and Taliban sources said.
The reported raids came as a US newspaper said that Washington was planning further drone attacks in Pakistan.
The drone programme, which the US administration reportedly views as "a success", is under evaluation as part of a review of the US military strategy in Pakistan and Afghanistan, The Wall Street Journal said.
|US intelligence officials are said to be drawing up a fresh list of drone targets [Reuters]
Intelligence officials from the US and Pakistan are composing a "fresh list of terrorist targets for drone strikes along the Pakistan-Afghanistan border", the daily said citing officials involved.
Adjustments could me made to "change the pace and size of the programme, and make some technical refinements in an effort to hit targets faster", the report said.
Accounts from Pakistani officials, residents and fighters say around 30 attacks have killed more than 300 people since August 2008.
The Pakistani government has protested to Washington that drone strikes violate its territorial sovereignty, saying that the attacks are counterproductive as the civilian casualties they often inflict have boosted support for fighters in the area.
The US in turn accuses Pakistan of not doing enough to crack down on fighters who cross the border to attack US and Nato troops in Afghanistan.
In a related development, The New York Times, citing American, Pakistani and other security officials, reported on Thursday that operatives in Pakistan's military intelligence agency are aiding the Taliban’s campaign in southern Afghanistan.
"The support consists of money, military supplies and strategic planning guidance to Taliban commanders," the newspaper said.
"There is even evidence that ISI [Directorate for Inter-Services Intelligence] operatives meet regularly with Taliban commanders to discuss whether to intensify or scale back violence before the Afghan elections."
Hundreds of Taliban and al-Qaeda fighters sought refuge in Pakistan's northwest tribal region after the US-led invasion of Afghanistan toppled the Taliban government in late 2001.