PHNOM PENH, May 10 (FN) — Cambodian Prime Minister Hun Sen on Tuesday defended security measures the government took against protesters clad in black during a so-called "Black Monday Campaign, " saying that the measures aimed to maintain the country's hard-won peace.

Anti-riot police on Monday prevented about 40 black-dressed human rights activists and land rights activists from marching to a planned protest at Prey Sar prison on the outskirts of Phnom Penh and detained eight of them, including local rights group Licadho deputy director and two foreigners — a German man and a Sweden woman who also work for Licadho.

The eight detainees were freed on Monday evening after they agreed to sign contracts promising not to do such an illegal protest again.

The group launched the campaign to demand the government to release five human rights defenders, who were jailed late last month on charges of bribing a witness in a sex scandal case, but the government said that the group's campaign was designed to cause chaos and unrest in the society.

"The government has obligations to maintain peace and political stability for the country; wrong-doers must take responsibility before the law," Hun Sen said during a university graduation ceremony here.

"No matter what color they use, if they break the law, legal action will be taken against them," he added.

The prime minister said the government would not bow to their pressures through protests and advised the protesters to hire smart lawyers to defend the perpetrators in court rather than protest.

Meanwhile, Hun Sen also warned a person, whom he did not give identity, for sponsoring black T-shirts for protesters.