ISLAMABAD, Pakistan  An airstrike believed to have been carried out by a United States drone killed at least 60 people at a funeral for a Taliban fighter in South Waziristan on Tuesday, residents of the area and local news reports said.

Details of the attack, which occurred in Makeen, remained unclear, but the reported death toll was exceptionally high. If the reports are indeed accurate and if the attack was carried out by a drone, the strike could be the deadliest since the United States began using the aircraft to fire remotely guided missiles at members of the Taliban and Al Qaeda in the tribal areas of Pakistan. The United States carried out 22 previous drone strikes this year, as the Obama administration has intensified a policy inherited from the Bush administration.

Before the attack on Tuesday, the Pakistani Army and Air Force had begun operations in South Waziristan against the forces of the Pakistani Taliban leader, Baitullah Mehsud. The group’s suicide bombings in major cities have terrorized Pakistanis for years.

In a serious blow to Pakistan’s effort, on Tuesday an assassin loyal to Mr. Mehsud shot and killed a rival tribal leader, Qari Zainuddin, whom the government had hoped to use as an ally in its campaign to corner the Taliban leader.