PESHAWAR, Pakistan (Reuters) -- A gunman shot dead a rival of Pakistani Taliban leader Baitullah Mehsud on June 23, dealing a potential blow to a government plan to defeat Al-Qaeda ally Mehsud.
The murder came as the military prepares an offensive against Mehsud, who has been accused of a string of bomb attacks, including the assassination of former prime minister Benazir Bhutto in 2007.
Separately, a U.S. drone aircraft fired a missile into a Mehsud stronghold in South Waziristan, near the Afghan border, military and intelligence officials said, but there was no word on casualties.
The murdered militant commander, known as Qari Zainuddin, had recently spoken out strongly against Mehsud. He was shot in the northwestern town of Dera Ismail Khan, police said.
"I confirm that Qari Zainuddin has been shot dead," Salahuddin, superintendent of police in the town, told Reuters.
It was not clear who was behind the killing, he said.
Militants are split into several factions in northwest Pakistan, some of which are rivals.
The military went on the offensive against Taliban fighters allied with Mehsud in the Swat Valley, northwest of Islamabad, in early May and they are in the final phase of that operation, the army has said.
The offensive in Swat came after Taliban gains raised fears for the future of nuclear-armed Pakistan, a vital ally for the United States as it strives to defeat Al-Qaeda and stabilize Afghanistan.
The government has also ordered an offensive against Mehsud in his South Waziristan stronghold near the Afghan border.
In recent days, the military has been launching air strikes on Mehsud's bases while soldiers have been securing the main road into the mountainous region populated by ethnic Pashtun tribes.
The United States has offered a reward of $5 million on information leading to Mehsud's location or arrest.
A Pakistani military official said the June 23 drone strike, the latest in a string of such attacks, was near the Mehsud stronghold of Makeen.
Zainuddin's strong statements against Mehsud in recent days had led to speculation authorities were encouraging him to stand up to his rival.
Suspicion for his murder is bound to focus on Mehsud, who was accused of being behind the killing of a prominent anti-Taliban cleric in a suicide bomb attack in the city of Lahore this month.
Government and military spokesmen were not available for comment.
A security analyst said Zainuddin's killing was a setback for government efforts against Mehsud, but authorities should not depend on Mehsud's rivals to get rid of him.
"He is Al-Qaeda number one in Pakistan," said Mahmood Shah, a former security chief in the country's Federally Administered Tribal Areas (FATA) in the northwest.
"This chap is too strong and a strong strategy is needed to deal with him."
The fighting in Swat sparked an exodus of civilians and aid workers fear a flow of villagers out of South Waziristan when fighting intensifies there.
Nearly 2 million people have fled fighting in the northwest, most since the army pushed into Swat, and another 40,000 or more have fled from South Waziristan even before the offensive begins.
The United Nations is appealing for $543 million in aid to avert a long-term humanitarian crisis but has received only 35 percent of that.
Pakistan is being kept afloat by a $7.6 billion International Monetary Fund loan, underscoring the need for outside help for the displaced.