A state security court in Sana'a imposed a media gag order Monday in the trial of three opposition leaders charged with stirring up violent protests in southern Yemen earlier this year.

Presiding judge Muhssien Alwan issued the order at the start of the second hearing into the case, saying that the gag order applied to both local and foreign media.

Police officers guarding the court's gate prevented journalists from entering even before the judge issued the ban. When the highly publicized trial began on May 28, journalists were allowed into the courtroom.

Hassan Baoum, Yahya al-Shouaibi and Ali al-Gharib, all senior members of the opposition Yemeni Socialist Party, are charged with instigating civil disorder.

Protests and riots hit several southern Yemeni cities where disgruntled youths took to the streets in April to protest what they called discriminatory army recruiting policies against southerners.

The Yemeni authorities charge the three men incited violent protests and riots that hit several southern cities.

At least 13 people were killed and more than 70 were injured in clashes with security forces.

South Yemen was an independent state with a Marxist regime until 1990 when it united with northern Yemen. An attempt to restore the south's independence was crushed in 1994 following a civil war.

Groups representing people who had retired from army and government jobs in southern Yemen have staged a series of protests in past 12 months in demand of more rights and better services.

On Sunday, a court in southern Yemen convicted 22 people of instigating violent protests, handind down six-month suspended jail terms. The court acquitted 10 other men.

Prosecutors had charged the group with endangering the country's security through stirring up violent protests in April.