A special court in Bahrain has sentenced eight Shi'ite opposition activists to life in prison for plotting to overthrow the minority Sunni-led government during a protest movement earlier this year.

The activists handed life terms on Wednesday include the head of the Shi'ite opposition Haq party, Hassan Mushaima, Haq member Abdul Jalil Singace and the leader of Shi'ite Islamic movement Wafa, Abdul Wahab Hussein.

Bahrain's National Safety Court also sentenced 13 other activists to prison terms of two to 15 years on similar charges of sedition. One of those activists is Ibrahim Sharif, the Sunni leader of the secular Waed party, who received a five-year term. The 21 defendants have the right to appeal.

Witnesses say the prison sentences triggered protests in several Shi'ite villages around the capital, Manama, with protesters blocking roads and police responding by firing tear gas. Activists vowed to stage more protests later in the day.

U.S. State Department spokesman Mark Toner said Washington is concerned about the severity of the sentences and believes they are “at odds” with the universal rights of Bahrain's citizens.

Toner said the United States continues to urge Bahrain to abide by commitments to “transparent judicial proceedings” and to creating the conditions for a “meaningful, inclusive and credible” national dialogue. The Gulf state's ruling al-Khalifa family, which hosts a key U.S. naval base, plans to open talks with the Shi'ite-led opposition next week.

A spokesman for Bahrain's main Shi'ite opposition party, Wefaq, told a news conference Wednesday that the group has not decided whether to join the talks. Khalil al-Marzooq said Wefaq is concerned that a dialogue will not be possible if key opposition figures are not invited, or jailed for life.

Haq leader Mushaima returned to Bahrain from exile earlier this year after King Hamad bin Isa al-Khalifa pardoned him from a previous conviction for trying to overthrow the monarchy.

Two other Shi'ite activists sentenced to life in prison Wednesday also hold European passports: Abdulhadi al-Khawaja, a Danish citizen, and Mohammed Habib al-Muqdad, a Swede.

After the sentencing, one of the activists in the courtroom shouted, “We will continue our struggle.” Some relatives of the defendants shouted “God is great.” One female relative was dragged out of the chamber.

Bahrain says 24 people were killed during a wave of opposition protests in February and March, including several security personnel. Some of the protesters called for the ouster of the monarchy, while others called for the ruling family to grant majority Shi'ites a greater say in government.

Bahraini security forces cracked down on the protest movement with the help of troops from neighboring Gulf states. Bahrain has insisted it is open to dialogue and denied reports of humn rights abuses.