Pakistani opposition leader Imran Khan addresses his party supporters during a rally in Peshawar on Tuesday. AP
Khan retains widespread support despite his April ousting and has staged mass rallies across the country calling for early elections and railing against the government.
His speeches frequently draw top ratings on television, with highlights trending on social media in Pakistan.
On Tuesday night, however, YouTube was down across much of the country as Khan addressed a rally in Peshawar, with London-based internet outage monitor Netblocks confirming the disruption.
"Access was restored after the speech concluded," Netblocks told AFP.
YouTube has not commented on the matter, while a representative of the Pakistan Telecoms Authority said they had "no idea about it".
Last month the government's media regulatory body banned Khan's speeches from being broadcast live, on the grounds they were inciting unrest, but this week the high court ruled the order illegal.
Still, no TV channels broadcast Tuesday's speech.
On Wednesday Khan accused the government of censoring him, saying the move would damage the country's reputation.
"They are imposing complete blackout of my speeches not only from mainstream media but also by blocking YouTube," he tweeted.
"This fascist govt of cabal of crooks & their backers are willing to harm the interests of Pakistan simply out of fear of (his party) PTI's soaring popularity. Utterly callous & unacceptable."
Supporters of Pakistani opposition leader Imran Khanâ€™s Tehreek-e-Insaf party attend a rally in Peshawar. AP
Last month ARY News, a pro-Khan television station critical of the current government, was taken off air but a court last week also ordered the ruling illegal.
Another private TV channel, Bol News, was suspended last week â€” ostensibly for operating with an expired licence â€” and insisted later it was being "punished for showing what the government doesn't like".
Free speech campaigners have long criticised the creeping censorship and control of Pakistan's internet, printed and electronic media.
"It is digital martial law," said Usama Khilji, a digital rights activist.
Khan is due in court on Thursday for a hearing on one of a slew of cases and charges brought against him since he was booted from office by a vote of no confidence in the national assembly.
The country has a history of those in power using the police and courts to stifle their political opponents, and current premier Shehbaz Sharif also has several pending cases from when he was in opposition.
Pakistan's political crisis comes as the country grapples with the worst floods in its history, with some 33 million people affected by record monsoon rains that have left almost a third of the nation under water.