"The decision has been taken to block TikTok for accessing in Pakistan".
TikTok, along with dozens of other mostly Chinese apps, was banned in June at the height of India's border dispute with China. However, TikTok failed to comply with the instructions which forced the PTA to ban it in the country.
Mr Khan said this week he recognised "the vast potential of digital platforms like Facebook and the role that they can play in giving global opportunities to Pakistani youth", after he held talks with Sheryl Sandberg, Facebook's chief operating officer.
There were several complaints logged with the PTA regarding the same issue.
The statement said the PTA had issued a final notice to the online application in July and gave considerable time to respond and comply with the instructions for development of effective mechanism for proactive moderation of unlawful online content.
"The ban is unfair and unjustified. instead of banning the app the PTA should have called on TikTok to ban those users", he said of the "immoral" content.
The move announced by the national telecommunications body strikes an app which has rocketed in popularity in the past year and gained millions of young Pakistani followers.
Amnesty International slammed the ban on TikTok, saying that in the name of a campaign against vulgarity, people are being denied the right to express themselves online.
The app also faces the threat of being barred in the USA after officials said it posed a national security risk, and it has come under intense scrutiny in Australia. Negotiations are underway for Walmart Inc and Oracle Corp to take stakes in a new company, TikTok Global, that would oversee USA operations. The app has been banned from India, is facing off a ban in the U.S.