It would be the latest in a series of protest rallies since last month to press for Khan's release and agitate against the ruling coalition government, which the party calls illegitimate, saying it was formed after a fraudulent election.
Shipping containers have been placed to block Islamabad's entry and exit points, guarded by large numbers of police and paramilitary troops, the officials said, while police banned any gathering in the capital.
"If someone plans to storm Islamabad, we wouldn't let that happen," Interior Minister Mohsin Naqvi told a news conference late on Thursday.
He urged Khan's party to shift the rally to later dates, to avoid disrupting Islamabad's preparations to host a meeting of the Shanghai Co-operation Organisation (SCO) on Oct. 15 and Oct. 16.
Malaysian Prime Minister Anwar Ibrahim is visiting, to be followed by a high-profile Saudi delegation and Chinese Premier Li Qiang ahead of the conference, Naqvi said, adding, "We can't allow any chaos."
Any agitation in the capital would not send a good signal to the world ahead of the conference, Naqvi said.
Disregarding the appeal, Khan asked his supporters to gather outside parliament regardless of obstacles.
"I want you all to reach D-Chowk today for a peaceful protest rally," he posted on X on Friday, referring to a spot outside parliament. "This war has entered a decisive phase."
Even though Khan has been in jail since Aug 2023, candidates backed by him won the most seats in February's general election, though their numbers were insufficient to form a government.
His opponents, led by Prime Minister Shehbaz Sharif, formed a coalition government instead.
In a statement on Friday, Islamabad police warned they would take action against anyone attempting to disturb the peace in the capital, adding that any gathering had been banned.
Schools were shut and cellphone services suspended in Islamabad and the adjacent garrison city of Rawalpindi.
A telecoms official said cellphone services were blocked on directions from the interior ministry. A ministry spokesman did not respond to a request for a comment.
