Senegal's government has cut access to mobile internet services in certain areas because of deadly rioting in which "hateful and subversive" messages have been posted online, it said in a statement on Sunday.

The West African country has been rocked by three days of violent protests in which 16 people have died, one of its deadliest bouts of civil unrest in decades.

Last week, the government limited access to certain messaging platforms, but many people were able to bypass the outage with the use of virtual private networks that mask the location of the user. It extended the outage on Sunday to include all data on mobile internet devices in certain areas and at certain times, the statement said.

It did not specify which areas were impacted or at what times, but residents across Dakar said they were unable to access the Internet without a wifi connection on Sunday afternoon, a time of day when protests have generally started to gather steam.

"Because of the spread of hateful and subversive messages ... mobile Internet is temporarily suspended at certain hours of the day," the statement said.

The catalyst for the unrest was the sentencing on Thursday of popular opposition leader Ousmane Sonko to two years in jail, which could prevent him from running in the February presidential election.

Protesters have also been angered by President Macky Sall's refusal to rule out running for a third term. Senegal has a two-term presidential limit.

Internet cuts to stifle dissent are common in Africa and date back to the 2011 Arab Spring when rulers in Egypt, Tunisia and Libya sought to control the spread of information. Since then Gabon, Gambia, Democratic Republic of Congo and others have done the same at times of instability.

Rights groups say the move violates freedom of speech. It can also dent already fragile economies.

"These restrictions ... constitute arbitrary measures contrary to international law and cannot be justified by security imperatives," Amnesty International said in a statement on Friday during the first wave of outages in Senegal.