Some 20,000 anti-government protesters took to the streets of Bahrain's capital, Manama, on Friday.
They were mostly Shi'ite protesters and they marched in northwestern Bahrain to demand reforms and release of prisoners.
The protesters say Bahrain is "a police state".
They denounced what they said was the "tyranny" in their country.
Their demonstration comes four days after 13 people were sentenced to life in prison for trying to kill two policemen during an illegal protest, according to their attorney.
The protest was one in a series of clashes that continue to erupt in this Sunni-ruled, Western-allied kingdom.
Bahrain's Shi'ite Muslims took to the streets in 2011 to demand more say in their country.
The island kingdom quelled early mass protests with help from neighboring Saudi Arabia, but sporadic unrest has continued.
