Drone strike, which killed Taliban chief, comes five years after US special forces killed Osama bin Laden in another Pakistani city.
Pakistan accused the United States on Sunday of violating its sovereignty with a drone strike targeting the leader of the Afghan Taliban, in perhaps the most high-profile US incursion into Pakistani territory since the 2011 raid to kill Osama bin Laden.
Afghanistan said the attack killed Mullah Akhtar Mansour, which, if confirmed, could trigger a succession battle within an insurgency that has proved resilient despite a decade and a half of US military deployments to Afghanistan.
Afghan Taliban commander Sirajuddin Haqqani, a possible successor to Mansour, would likely prove an even more implacable foe of Afghan government forces and their US allies.
Still, the Saturday drone strike showed the United States was prepared to go after the Taliban leadership in Pakistan, which the government in Kabul has repeatedly accused of sheltering the insurgents.
Pakistan protested on Sunday, saying the US government did not inform Prime Minister Nawaz Sharif beforehand.
"This is a violation of Pakistan's sovereignty," Sharif told reporters in London.
US official, speaking on condition of anonymity, acknowledged that Washington only notified Pakistan after the strike.
It was unclear how long Mansour might have been inside Pakistan before the strike. Pakistan's Foreign Ministry disclosed that a passport found at the site of the strike, bearing a different name, carried a valid Iranian visa.
These pictures have been shared on Twitter and Facebook, confirming he came from Iran and was also carrying Pakistani documents.
The Foreign Ministry added that the purported passport holder was believed to have returned to Pakistan from Iran on Saturday, the day of the drone strike targeting Mansour. Photos of the passport, bearing the name Wali Muhammad, seen by Reuters showed a passing resemblance to some of the old photos available of Mansour.
If it is confirmed that Mansour had travelled to Iran before his death, it would raise new questions about the Taliban's use of neighbouring territories, including Iran.
People on social media have already started to wonder what the Taliban leader was doing in Iran. And why wasn't he killed there.