Algerian opposition supporters clashed with police during a banned protest in the capital, Algiers, on Saturday.
The protest comes about a week after a wave of demonstrations in neighbouring Tunisia forced that country's president to flee.
Police with batons and shields surrounded the headquarters of the opposition Rally for Culture and Democracy (RCD) party and blocked the exit, while they prevented protesters in front of the building from marching to the National Assembly as planned.
Photo galleryPolice break up banned protest
At least 19 people were injured in the pro-democracy rally, the government said, but an opposition party official put the figure at more than 40.
"I am a prisoner in the party's headquarters," Said Sadi, a former presidential candidate who leads the RCD, said through a megaphone from a balcony window.
Demonstrators shouted "Boutef out!" referring to President Abdelaziz Bouteflika — echoing cries against Tunisian President Zine El Abidine Ben Ali before he fled Jan. 14 to Saudi Arabia amid huge street protests in Tunisia.
Public gatherings in Algeria have been banned since 2002, but RCD, the country's largest opposition party, said around 300 protesters had defied the ban in order to speak out against unemployment and lack of freedom in the North African country.
Algeria is a former French colony, which is emerging from a conflict between security forces and Islamists that killed an estimated 200,000 people from 1991 to 2002.
Tunisia was shaken by a series of riots in the beginning of the year. Protesters took to the streets to speak out against government corruption, unemployment and a spike in basic food prices.