Dubai: Bahraini protesters poured back to the streets after a security court sentenced eight senior opposition leaders to life in prison.

Security forces used tear gas to drive back hundreds of marchers trying to reach a central square in the capital Manama, which was once the hub of their protests. In other areas, protesters gathered in the streets but were held back by riot police. No injuries were reported.

Two major rallies

Bahrain has allowed two major rallies this month by the main opposition party, but the confrontations on Wednesday were among the biggest challenges to security forces since martial law-style rule was lifted June 1.

In Washington, State Department spokesman Mark Toner said the U.S. was "concerned about the severity" of the sentences and the use of the military-linked security courts. He noted that President Barack Obama said in May that "such steps are at odds with the universal rights of Bahrain's citizens."

"We continue to urge the Bahraini government to abide by its commitment to transparent judicial proceedings, conducted in full accordance with Bahrain's international legal obligations, and to create the conditions for a meaningful, inclusive and credible dialogue," he said.

Government's statement

Bahrain's government said in statement late Wednesday that the convicted activists were responsible for "bringing the country to the brink of total anarchy" with a wave of marches and sit-ins earlier this year.

"Today's sentencing sends a message that law and order will be preserved," the statement said, pledging to guard against "attempts to overthrow the regime."

The official Bahrain News Agency said those sentenced to life include prominent political figures Hassan Mushaima and Abdul Jalil Al Singace and rights activist Abdul Hadi Al Khawaja. Mushaima returned from self-exile in London earlier this year after Bahrain's leaders promised to erase old charges of opposing the state.

Pro-reform activist Ebrahim Sharif, received five years in prison, while other sentences ranged from two to 15 years. The sentences can be appealed.

A leading opposition figure cast doubt on whether talks can get under way.

Dialogue in an open atmosphere

"We should conduct the dialogue in an open atmosphere, not when people are being arrested," said Khalil Al Marzooq, who was among the 18 parliament members who staged a mass resignation to protest the crackdowns earlier this year.

The charges at the latest security court trial show the depths of the tensions.

The activists were convicted of trying to overthrow Bahrain's 200-year-old monarchy and having links to "a terrorist organization abroad", an obvious reference to claims that Iranian-backed Hezbollah is behind the unrest.

Eight received life sentences while 13 others received shorter prison terms apparently because they weren't considered leaders.