Opposition leaders said some of the deaths occurred after security forces beat and then opened fire on demonstrators in Somaliland's capital Hargeisa and two other towns.
Abdirahman Cinro, a presidential hopeful and former head of Wadani, one of the two opposition political parties championing the protests said six people were killed.
"The demos will continue and it is just the beginning until we get full democratic space and freedom from dictatorship and bad leadership," he said.
Videos shared on social media showed protesters throwing stones and burning tires in the streets of Hargeisa, while some security forces fired weapons and tear gas. Reuters was unable to independently authenticate the videos.
During the clashes dozens of security personnel were injured by protesters who were armed with knives, catapults and clubs, said Abdi Hassan Mire, deputy commander of the Somaliland police. Some carried weapons and fired bullets, he said.
Property and vehicles were also destroyed, according to police.
At least 100 people suspected of involvement in the clashes were arrested and will be charged soon, Ibrahim Abdi Haji, head of operations in Somaliland Police, said.
The majority of those who were injured, according to Muse Bihi Abdi, president of Somaliland, were security forces "who were attacked with clubs, metal bars, and stones." He did not say whether those killed were civilians or security personnel.
"We shall not allow chaos and demonstration in any town or in any village. They will be confronted. Unauthorized violent demonstration to destroy the nation will not be accepted."
Somaliland broke away from Somalia in 1991 but has not gained widespread international recognition for its independence. The region has been mostly peaceful while Somalia has grappled with three decades of civil war.
In a statement on Thursday six foreign diplomatic missions, including the U.S., U.K. and E.U., condemned what they called "excessive use of force" during the demonstrations.