Messaging services including Facebook, Whatsapp, Twitter and Tango have been cut off in Burundi amid protests over the president seeking a third term.
The regulator ordered telecoms operators to block mobile access to certain sites, reports AFP.
The government has banned protests, deployed the army and shut down the main independent radio station.
There have been days of protests over President Pierre Nkurunziza's decision to stand for re-election in June.
Social media messaging services have been used to coordinate the protests which are the biggest in Burundi since the civil war ended in 2005.
African Public Radio, known as "voice of the voiceless", is one of three radio stations whose live broadcasts have been stopped. The government said the radio station was disrupting the peace.
The BBC's Maud Jullien in the capital Bujumbura says people are defying the ban on protesting for a fourth day.
Mr Nkurunziza, a former rebel leader, has warned that anyone who wants to create problems for the governing party would find himself "in trouble".
At least three people were killed on Sunday as police dispersed crowds with live ammunition.
Under the constitution, presidents can only be elected to two terms in office but Mr Nkurunziza's allies say his first term does not count as he was appointed by parliament.
Burundi's senate has announced that the constitutional court will examine the legality of the bid.
Mr Nkurunziza has been in power since 2005, when a 12-year civil war officially ended.
More than 300,000 people died in the conflict between the minority Tutsi-dominated army and mainly Hutu rebel groups, such as Mr Nkurunziza's CNDD-FDD.