Pakistan's Prime Minister Shehbaz Sharif declared a day of mourning after Iranian media reported that president Ebrahim Raisi had died in a helicopter crash.
"Pakistan will observe a day of mourning and the flag will fly at half mast as a mark of respect for President Raisi and his companions and in solidarity with Brotherly Iran," Shehbaz posted on X, formerly Twitter.
"I along with the government and people of Pakistan extend our deepest condolences and sympathies to the Iranian nation on this terrible loss," he added.
"The great Iranian nation will overcome this tragedy with customary courage."
The Pakistani leader hosted Raisi in Islamabad for a three-day visit in April in a bid to mend ties between the neighbours after they traded deadly strikes earlier this year.