KABUL, Afghanistan — After months of failed Pakistani efforts to broker peace talks with the Taliban, an American drone strike against the leader of the Afghan militants signaled a major break with precedent as the United States circumvented Pakistan in an effort to disrupt the strengthening insurgency, officials said on Sunday.

The Afghan intelligence agency said Sunday that the Taliban leader, Mullah Akhtar Muhammad Mansour, had been killed in the strike in the restive Pakistani province of Baluchistan. The United States announced the strike Saturday but could not confirm that Mullah Mansour had been killed.

Although there was still no official reaction from the main Taliban spokesman, some Taliban commanders on Sunday denied the reports, saying their leader was not in the area of the strike.

Even if Mullah Mansour was not killed, the attack was significant, as it is believed to be the first American drone strike in Baluchistan, the de facto headquarters of the Afghan Taliban, after years of such attacks in other Pakistani and Afghan areas.