A New York-based press watchdog, the Committee to Protect Journalists (CPJ), said three Egyptian journalists were arrested for covering protests which followed a football match in Cairo on Friday night.
The group also said that several websites were disrupted, including those of news outlets BBC and the US-government funded Al-Hurra television.
Safaa Faisal, Egypt''s BBC bureau chief, confirmed to AFP that the news site was inaccessible on Monday without any specific explanation from authorities.
However, Makram Ahmed, head of Egypt''s Supreme Media Regulation Council, had told BBC that authorities may have blocked some sites including BBC Arabic for "inaccurate coverage" of the protests.
Many users have also reported difficulties with accessing popular app Facebook Messenger, according to CPJ.
"Egyptian authorities must release all journalists arrested for their protest coverage, unblock news websites and communication apps, and allow journalists to report freely and safely," it said.
In a related development, the Civil Democratic Movement, a coalition of liberal and leftist opposition parties, called for a "national dialogue" and for the release of all those arrested over the protests.
Rights groups say around 600 people have been arrested, including several opposition leaders, activists and family members detained from their homes.
Amnesty International said security forces had "carried out sweeping arrests of protesters, rounded up journalists, human rights lawyers, activists and political figures in a bid to silence critics and deter further protests from taking place".
The BBC and Al-Hurra had been added to a list of 513 other websites already blocked in Egypt, it said.
On Sunday, award-winning human rights lawyer Mahienour El-Massry was taken into custody after she attended judicial investigations into the arrests of protesters.
Hundreds of Egyptians took to the streets Friday and Saturday in Cairo and other cities for the rare anti-Sisi protests, held in defiance of a ban on demonstrations.
The dissent on the streets came on the back of an appeal by an exiled Egyptian businessman in Spain to topple Sisi after levelling corruption accusations against him. (AFP)