Cambodian riot police on Monday used smoke grenades and electric batons to disperse demonstrators in the capital demanding a government licence for an independent television station.
In the latest of a series of violent crackdowns on public dissent, scores of riot police broke up the protest in front of the Ministry of Information, according to an AFP reporter at the scene.
About 300 protesters led by prominent government critic and radio station owner Mam Sonando had marched to the ministry to demand the licence.
Cambodia has been accused of only granting television licences to pro-government media.
Protesters and journalists -- including an AFP photographer -- were hit by police batons and several were injured during the crackdown, according to rights activists.
"Other radio stations have a TV station, why can't my Beehive radio station?" Sonando, who is a prominent government critic, told AFP.
Activist Am Sam Ath of local rights group Licadho condemned the crackdown on the protesters as a "serious violation of human rights".
Phnom Penh City Hall spokesman Long Dimanche said police dispersed the protest because it had not been permitted and could have led to violence.
"It was illegal demonstration. So the authorities just implemented the law," he said.
Sonando, who has dual Cambodian-French citizenship, was convicted in October 2012 on charges including insurrection and inciting people to take up arms against the state.
He was released from jail last March after a court cleared him of a secessionist plot, slashing his 20-year jail term and ordering his release from prison.
Authorities have quelled recent street protests against strongman Prime Minister Hun Sen.
His government has indefinitely banned demonstrations in the capital by the opposition, which accuses him of vote-rigging in a general election last year.
Baton-wielding police clashed Sunday with protesters -- including Buddhist monks -- demanding higher wages for garment workers and the release of 23 people arrested during a recent bloody crackdown on striking garment workers, which left at least four civilians dead.
Hun Sen faces mounting criticism by rights groups of his government's suppression of street protests intended to challenge his nearly three-decade rule.
US-based Human Rights Watch (HRW) called on the United Nations to condemn a "rights onslaught" in Cambodia.
"Hun Sen's government violates human rights on a daily basis by violently preventing the opposition, trade unions, activists and others from gathering to demand political change," HRW director Juliette de Rivero said in the statement.
Cambodia is due to face the UN Human Rights Council's Universal Periodic Review (UPR) in Geneva on Tuesday.
"Countries at the Human Rights Council should condemn this brutal crackdown and insist the Cambodian government engage in serious reforms," de Rivero said.