Thousands of anti-government protesters burned tires and threw firebombs and stones at riot police in Bahrain on the second anniversary of the intervention by a Saudi-led force which helped crush a pro-democracy uprising in the Gulf island.
The clashes on Thursday were the worst in several weeks and served a reminder that elements of the opposition have yet to buy into slow-moving talks with government officials.
Police fired stun grenades at the demonstrators during the clashes in the mainly Shia neighbourhoods surrounding the capital, Manama.
Starting early in the morning, the mostly young demonstrators blocked roads leading into scores of Shia villages to prevent security forces from entering.
Bahrain's Shia majority has been seeking a greater political voice in the Sunni-ruled kingdom, which is home to the US Navy's 5th Fleet.
The main Shia opposition group, Al Wefaq, said 35 protesters were wounded in the clashes, including three critically, in what it called a "systematic policy carried out under high, official orders to use violence against peaceful pro-democracy protesters".
It also accused police of using live ammunition and bird shot against some protesters.
"This is an unforgettable day," said Maki Ali, an 18-year-old demonstrator from Bilad Al Qadeem, west of the capital, Manama.
"I remember well how the Saudis with United Arab Emirates intervened in my country's internal affairs. They supported the government killing."
Saudi and other Gulf troops were deployed in Bahrain to help the Western-backed Sunni monarchy quell a wave of anti-government protests demanding a greater role for the country's Shia majority.
Ameena Mohamed Hussain, a 21-year-old from the village of Diah, said she still carried a lot of anger from that day two years ago.
More than 60 people were killed in more than two years of unrest inspired by the Arab Spring.
"This government doesn't hear our voices and I can't forgive what the (Gulf) troops did in my country," she said.
"They supported our evil government."
'Acts of terrorism'
The state-run Bahrain News Agency did not mention the anniversary, but reported that several villages saw "acts of terrorism committed by saboteurs for the purpose of intimidating and jeopardising the lives of citizens," including burning stolen cars and block roads with boulders and pylons.
It said a "number" of policemen were injured when protesters attacked them with petrol bombs and detonated several homemade explosives.
"All these acts of terrorism were committed by outlaws in order to prevent citizens and residents from going to workplaces or performing their routine daily errands," the news agency said.
Al Wefaq and other main Shia factions opened talks with government officials and Sunni envoys last week, but some hardline Shia groups oppose dialogue.
Many Shias fear that the negotiations process will not weaken the monarchy's hold on power.
Opposition groups have demanded that the ruling dynasty relinquish much of its sweeping authority over the country's affairs, including picking all key government and military posts.