Police arrested 108 people in the confrontations in Algiers, the capital, in which 27 officers were injured, police said, adding that four of the officers were in serious condition. No mention was made of civilians.
The clashes were between police and "delinquents infiltrated" into the protests, the reliable online publication TSA Algerie reported, citing the General Direction for National Security, known as the DGSN.
In an earlier statement, the DGSN said security forces arrested foreigners trying to raise tensions and push youth into "forms of radical expression" during protest marches. It did not say who or how many had been detained.
The statement also said that through the weeks of protests delinquents and others have been arrested among demonstrators with some trying to steal, harass or be aggressive, the official APS news agency reported.
The Algiers clashes tainted what have been peaceful nationwide protests that have been a source of pride for the North African nation whose population is trying to do away with the political system that has prevailed since independence from France in 1962.
Abdelaziz Bouteflika was forced to resign April 2, pressured by protests that began Feb. 22, and clinched when the powerful army chief firmly reiterated the demand. Friday's protests were the first since the interim leader, Abdelkader Bensalah, announced this week the date for presidential elections — July 4.
"Everybody get out," protesters chanted, reflecting the demand that the former president's entourage, widely viewed as corrupt, leave, and their dream of a new Algeria. Tension mounted in late afternoon when some protesters tossed rocks and bottles at police at a small square that serves as a key point for gatherings. Police moved in with tear gas. An Associated Press photographer saw an officer firing what apparently were rubber bullets.
Security forces then went after crowds with tear gas at key points around the city center where protesters gather, including the iconic central post office, the main gathering point for the pro-democracy movement. Two helicopters flew above the acrid smoke that sent crowds running.
When tear gas was fired at protesters at the junction of a boulevard and a road leading to the president's office, cries of "Allaoh akbar" and "Peaceful! Peaceful!" were heard. Volleys of tear gas then targeted another main axis through the city center and eventually moved to the post office.
The streets were packed with protesters waving Algerian flags. Some shouted "Authorities - Assassins!" and surrounded a water cannon truck, with some appearing to hit it. Much of the anger was focused on the interim president, Bensalah, seen as a remnant of the old regime.
"Bensalah, get out!" the protesters shouted, as a river of people adorned in green, white and red Algerian flags wove through the city. "His Majesty the People orders you to resign tomorrow!" read one sign. Another called Bensalah, and the prime minister and the constitutional council president "Residue of the Bouteflika System."
Anger is also mounting at military chief Gen. Ahmed Gaid Salah, who was instrumental in Bouteflika's departure but then threw his support behind Bensalah. Protesters called for a truly independent leadership structure and a technocratic government to lead a political transition.
"It's been eight weeks since I've seen my family, I'm so tired," said one police officer, Salim, as he choked back tears. The 32-year-old spoke to The AP on condition his last name not be used for fear of repercussions. "I never thought I'd find myself confronting my compatriots to stop them from protesting. They're my age."
Algeria's protest movement has been driven by young people frustrated with corruption and unemployment and who want a new generation of leaders. "Mentalities have to change. It's not just about going out and shouting, which is good and important, but taking action is important too," said Imad Touji, a 22-year-old student.
"We really need to change things in a concrete way."
Mosa'ab Elshamy in Algiers contributed.