Demonstrators calling for democratic reform clashed with police Friday in Shiite villages near Manama ahead of an international forum on Middle East security, witnesses said.
A Shiite-led uprising to demand changes in the Sunni-ruled kingdom was crushed in March 2011 but almost weekly protests against the authorities have been since staged in Shiite villages around Manama.
On Friday, dozens of protesters, mostly youths, clashed with police in the villages of Sanabis, Deraz, Sitra and Diya, hurling stones and petrol bombs at the security forces, witnesses said.
The protesters also blocked roads with burning tyres, the witnesses said.
Police responded by firing tear gas and sound bombs to disperse them, they added. There were no immediate reports of casualties.
In the village of Sar near Manama, thousands of people took to the streets at the call of the main Shiite opposition bloc Al-Wefaq to protest against a crackdown on opposition activists.
Witnesses said the protesters held up pictures of jailed Shiite opposition leaders and banners carrying "messages" for top officials, including from Britain and the United States, due to attend the two-day Manama Dialogue forum that opens Friday evening.
"To those meeting at the Manama Dialogue (conference): Are you aware that there are female detainees in Bahraini jails?" read one banner.
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"Why do you support democracy for people of other countries... (and not) in Bahrain?" read another banner.
British Foreign Secretary William Hague is due to deliver the keynote address at the annual forum that focuses on Middle East security when it opens at around 1800 GMT.
US Defence Secretary Chuck Hagel will also give a speech on Saturday, the second day of the forum which is organised by the International Institute for Strategic Studies.
Witnesses said police beefed up security in Shiite villages ahead of the forum and set up checkpoints on roads leading to the hotel hosting the four-day conference in the Seef area near the capital.
Bahraini authorities have banned protests from taking place in Manama.
At least 89 people have been killed since the protests began, according to the International Federation for Human Rights.
Authorities arrested hundreds of activists, mostly Shiites, in the wake of the 2011 uprising,dozens have faced trials and as many have been convicted to jail terms.
Rights groups have denounced the arrests and trials in Bahrain.
Bahrain is home to the US Fifth Fleet, a crucial naval hub that oversees aircraft carriers and other warships patrolling the strategic Gulf sea lanes.
Washington views Bahrain of "great strategic importance", but has withheld some military assistance as part of an effort to urge Manama "to lift restrictions on civil society" and "engage in a deliberate reform process," US National Security Adviser Susan Rice said Wednesday.