Witnesses said police fired tear gas at marchers trying to reach a central square in Bahrain's capital, Manama, that was once the hub of their campaign for greater freedoms, which began in February as the political tumult in the Arab world spread to the Gulf.
After the court ruling, Shiite crowds blocked roads with sand piles and called for the protest marches, which also took place in Shiite villages on the capital's outskirts. It was the first serious unrest after months of a security lockdown by military and police units in Bahrain, a key American military ally that is home of the U.S. Navy's 5th Fleet.
The court handed down life sentences for eight Shiite activists and long jail terms for 13 others. They were convicted of trying to overthrow Bahrain's 200-year-old monarchy and of having links to "a terrorist organization abroad."
"It's a political verdict," said Nabeel Rajab, president of the Bahrain Center for Human Rights. "All those convicted today were targeted because of their activities to bring about change and democracy in Bahrain."
Angry crowds took their grievances back to the streets after the verdict despite the strengthened police presence around the Gulf island.
Shiites account for 70 percent of Bahrain's population, but claim they face systematic discrimination such as being barred from top government and political posts.
The protests in Bahrain have claimed at least 31 lives since February and put U.S. officials in the difficult position of denouncing the violence while standing by the allied rulers.
The kingdom's rulers fear that any gains by Bahrain's Shiites could open new footholds for influence by Iran, a predominantly Shiite country that is a main regional rival of the Sunni Arab-led nations just across the Gulf. Bahrain also accuses Iranian-backed Hezbollah of having a role in the protests.
Shiite leaders in Bahrain have repeatedly denied any ties to Iran and accuse leaders of using the fears of Iranian string-pulling to wage crackdowns that have included hundreds of arrests and purges from jobs and universities.
Fourteen of the 21 convicted are in custody while the rest were sentenced in absentia by the security court, which was set up during martial law-style rule that was imposed in March. The emergency rule was lifted June 1, but the arrests and trials at a military-civilian tribunal with military prosecutors have continued.
The official Bahrain News Agency said those sentenced to life included prominent Shiite political figures Hassan Mushaima and Abdul Jalil al-Singace and rights activist Abdulhadi al-Khawaja. Mushaima returned from self-exile in London earlier this year after Bahrain's leaders promised to wipe away old charges of opposing the state.
Pro-reform activist Ibrahim Sharif - the only Sunni among the suspects - received five years in prison while other sentences ranged from two to 15 years. The sentences can be appealed in the same court within 15 days.
Sharif's wife, Farida Ghulam, said her husband cried out "Our people demand freedom" after the sentences were read.
Ghulam said al-Khawaja then shouted: "We will continue our struggle." His daughter, Zainab, was dragged from court by female guards after she yelled "Allahu akbar," or "God is great," Ghulam said.
The sentences could imperil U.S.-backed efforts by Bahrain's Sunni leaders to open talks next week with Shiite groups, which have demanded an end to the political trials and the withdrawal of a Saudi-led regional force helping prop up the Bahrain ruling family.
"We should conduct the dialogue in an open atmosphere, not when people are being arrested," said Khalil al-Marzooq, who was among the 18 Shiite parliament members who staged a mass resignation to protest the crackdowns earlier this year.
The verdicts could also bring some direct diplomatic fallout. At least two of those sentenced to life also hold European passports: al-Khawaja, who is a Danish citizen, and Mohammed Habib al-Muqdad, who has Swedish citizenship.
Hours before the court session, the state news agency announced that the government had sent out 300 invitations to political parties and individuals for the proposed dialogue to begin July 1. The report did not name any of the potential participants.
"The dialogue aims at bringing together the various segments of the Bahraini society to present the people's views and demands for further reform in the country," the report quoted Parliament Speaker Khalifa bin Ahmed al-Dhahrani as saying. Al-Dhahrani is in charge of the talks.
