Supporters of Senegal's firebrand opposition leader Ousmane Sonko condemned police brutality on Sunday after clashes over his recent court conviction left at least 16 people dead and more than 350 demonstrators injured.

The violence erupted on Thursday when Sonko was sentenced to two years behind bars in a case he says was designed to stop him running for president next year.

In total, 78 seriously wounded people were taken to health centres, it added.

Supporters of Sonko and President Macky Sall have traded blame for the violence and deaths.

On Sunday, Sonko's PASTEF-Patriots party condemned "the murderous repression by defence and security forces", accusing the government of deploying "private militias".

It urged people to "defend themselves in any way they can and fight back".

The official death toll is 16, but PASTEF-Patriots said 19 demonstrators had been killed.

The government has restricted access to social media and on Sunday decided to "temporarily" cut mobile data internet on phones, saying "hateful and subversive messages" were being shared.

There were more signs of a return to calm on Sunday, with fewer officers on the streets and quiet in several Dakar neighbourhoods that saw violence earlier in the week.

The interior ministry said there was a "clear drop in tension and arrests".

On Saturday, Interior Minister Antionie Diome said around 500 people had been arrested since Thursday.

He said he suspects "foreign influence" is behind what he called an "attack" against Senegal, without elaborating.

Sonko, a 48-year-old former tax inspector, has spoken out against debt, poverty, food insecurity, under-funded health and education systems and corruption.

He was initially charged with rape but was convicted on a lesser charge of morally "corrupting" a young woman.

His conviction may take him out of the running for the 2024 poll.

He was tried in absentia and has yet to be taken into custody for his jail term, which is predicted to stoke further tensions.

He is presumed to be at his Dakar home, where he has been blocked in by security forces since last weekend. He previously alleged he was being "illegally held".

Sonko's ongoing legal woes have prompted rare flare-ups of violence in Senegal, typically a bastion of stability in West Africa, and foreign allies have urged a return to calm.