A passport found at the site of a U.S. drone attack targeting Afghan Taliban leader Mullah Akhtar Mansour bears the name of a Pakistani man named Wali Muhammad and carries a valid Iranian visa, the Pakistani Foreign Ministry said on Sunday.

The ministry did not directly comment on the possibility that Mansour might have been travelling under another name.

Afghanistan’s spy agency said it was sure Mansour had been killed in the attack, but Prime Minister Nawaz Sharif told reporters in London that Pakistan was unsure if Muhammad was “Mullah Mansour or someone else”. He called the attack “a violation of Pakistan’s sovereignty”.

Saturday’s strike, which U.S. officials said was authorised by President Barack Obama and involved multiple drones, took place in Pakistan’s remote Baluchistan area near the Afghan border. Pakistan said the air strike had destroyed a car carrying two people, and that Sharif had not been told about it in advance.