DAKAR - Fresh clashes broke out on Saturday between opposition supporters and Senegalese police in parts of the capital Dakar, the third day of protests in the West African nation sparked by the prosecution of an opposition leader.

Protesters took to the streets in the evening, setting up barricades and burning rubbish in the HLM district. Police there and in the Ngor residential neighbourhood fired tear gas in an effort to disperse angry crowds.

Gas stations and a supermarket were looted overnight and several districts were strewn with rubble and burned tyres.

"The police couldn't do anything... The police had to leave after several attempts to control the crowd with tear-gas grenades", said resident Khadija at a supermarket littered with broken shelves, mud and trash in Dakar's densely populated Grand Yoff neighbourhood.

Police said the death toll in violence since Thursday rose to 15 after six deaths on Friday, making the protests among the deadliest in recent decades. The presidency said two members of the security forces were among those killed.

The catalyst for the latest unrest was the sentencing on Thursday of opposition leader Ousmane Sonko in a two-year-old rape case. His supporters say the prosecution was politically motivated and he denies any wrongdoing.

On Thursday, he was acquitted of rape but found guilty of corrupting a minor and sentenced to two years in prison. That sentence could prevent him from running in the February presidential election, and protesters have heeded his call to challenge authorities.

The government has enlisted the army to back up riot police stationed around the city. The Dakar district of Ouakam appeared calm on Saturday evening but more than a dozen soldiers guarded a ravaged gas station there.

Abdou Ndiaye, the owner of a nearby corner shop, said he had closed early the two previous days and opened late on Saturday, fearful of the unrest.

"We are so scared because you don't know when the crowds will come, and when they come they take ... your goods, they are thieves," he said in a storeroom stacked with sacks of food and household items.

Senegal, long considered one of the region's most stable democracies, has seen sometimes violent opposition demonstrations sparked by Sonko's court case as well as concerns that President Macky Sall will try to bypass a two-term limit and run again in February.

Sall has neither confirmed nor denied this.

(Additional reporting by Edward McAllister, Bate Felix, Cooper Inveen; Writing by Alessandra Prentice; Editing by Mark Potter, Christina Fincher and Cynthia Osterman)