If confirmed, Mehsud's demise would be a major boost to Pakistani and U.S. efforts to eradicate the Taliban and al-Qaida.
Mehsud has al-Qaida connections and has been suspected in the killing of former Pakistani Prime Minister Benazir Bhutto. Pakistan views him as its top internal threat and has been preparing an offensive against him. The U.S. sees him as a danger to the war effort in Afghanistan, largely because of the threat he is believed to pose to nuclear-armed Pakistan.
The missile strike hit the home of Mehsud's father-in-law in Pakistan's South Waziristan tribal region early Wednesday. Intelligence officials say Mehsud's second wife was among at least two people killed, and Mehsud associates have claimed he was not among the dead.
Pakistan army spokesman Maj. Gen. Athar Abbas cautioned the reports of Mehsud's death were still unconfirmed. "We are receiving reports and probing," he said.
A senior Pakistani intelligence official said phone and other communications intercepts -- he would not be more specific -- have led authorities to suspect Mehsud was dead, but he also stressed there's no definitive evidence yet. He spoke on condition of anonymity because he was not authorized to speak on the matter publicly.
The U.S. government was also looking into the reports, according to a U.S. counterterrorism official. The official indicated the United States did not yet have physical evidence -- remains -- that would prove who died. But he said there are other ways of determining who was killed in the strike. He declined to describe them.
The two U.S. officials spoke on condition of anonymity because they were not authorized to discuss the matter publicly.
The U.S. and Pakistan will conduct DNA testing on the body to try to confirm it is Mehsud, The Wall Street Journal reported, citing an unnamed U.S. defense official. The tests will use DNA samples taken from Mehsud's family members, and results could take anywhere from days to weeks, the newspaper reported.
For years, the U.S. has considered Mehsud a lesser threat to its interests than some of the other Pakistani Taliban, their Afghan counterparts and al-Qaida, because most of his attacks were focused inside Pakistan, not against U.S. and NATO troops in Afghanistan.
That view appeared to change in recent months as Mehsud's power grew and concerns mounted that increasing violence in Pakistan could destabilize the U.S. ally and threaten the entire region.
In March, the State Department authorized a reward of up to $5 million for the militant chief. And increasingly, American missiles fired by unmanned drones have focused on Mehsud-related targets.
While Mehsud's death would be a big blow to the Taliban in Pakistan, he has deputies who could take his place. Whether a new leader could wreak as much havoc in Pakistan as Mehsud could depends largely on how much pressure the Pakistani military continues to put on the Taliban network, especially in South Waziristan.
Pakistan's record is spotty on that front. It has used both military action and truces to try to contain Mehsud over the years, but neither tactic seemed to work, despite billions in U.S. aid aimed at helping the Pakistanis tame the tribal areas.
Mehsud was not that prominent a militant when the U.S. invaded Afghanistan in 2001 after the Sept. 11 attacks, according to Mahmood Shah, a former security chief for the tribal regions. In fact, Mehsud has struggled against such rivals as Abdullah Mehsud, an Afghan war veteran who had spent time in U.S. custody in Guantanamo Bay.
A February 2005 peace deal with Mehsud appeared to give him room to consolidate and boost his troop strength tremendously, and within months dozens of pro-government tribal elders in the region were gunned down on his command.
In December 2007, Mehsud became the head of a new coalition called the Tehrik-e-Taliban Pakistan, or Pakistan's Taliban movement. Under Mehsud's guidance, the group has killed hundreds of Pakistanis in suicide and other attacks. He is believed to have as many as 20,000 fighters at his beck and call, among them a steady supply of suicide bombers.
Analysts say the reason for Mehsud's rise in the militant ranks is his alliances with al-Qaida and other violent extremist groups. U.S. intelligence has said al-Qaida has set up its operational headquarters in Mehsud's South Waziristan stronghold and the neighboring North Waziristan tribal area.
Mehsud has no record of attacking targets in the West, although he has threatened to attack Washington.
However, he is suspected of being behind a 10-man cell arrested in Barcelona in January 2008 for plotting suicide attacks in Spain. Pakistan's former government and the CIA have named him as the prime suspect behind the December 2007 killing of former Prime Minister Benazir Bhutto. He has denied a role.
He also has withstood threats from within Taliban ranks. A few weeks ago, Qari Zainuddin, the leader of a renegade Pakistani Taliban faction who had criticized Mehsud's tactics, was shot to death -- allegedly on Mehsud's orders.
In June of this year, Pakistan said it would launch an offensive against Mehsud in South Waziristan.
In the weeks that have followed, the army has relied heavily on airstrikes to target areas under Mehsud's control, but it has never quite gone full-scale with the offensive. Meantime, the missile strikes continued, raising speculation that the U.S. might get him first. Pakistan publicly opposes the missile strikes, saying they anger local tribes and make it harder for the army to operate. Still, many analysts suspect the two countries have a secret deal allowing the strikes.------
Associated Press writers Nahal Toosi in Islamabad and Pamela Hess in Washington, D.C. contributed to this report.