Bahraini police headed off a protest Wednesday against the Gulf kingdom's Sunni rulers that Shiite-led opposition activists called for near the US embassy in defiance of a ban.
They fired tear gas and buckshot at hundreds of protesters who ventured out in several Shiite villages, witnesses reported.
The interior ministry said police deployment, which began on Tuesday, was aimed at "preserving security and order, and to guarantee an easy flow of traffic."
Al-Wefaq, the main opposition formation, said police had blocked roads leading to Shiite-populated villages with barbed wire and concrete blocks.
It accused the authorities of turning some areas into a "vast prison for inhabitants," and also published pictures of closed shops in several areas.
The deployment prevented protesters from reaching the spot designated by the Bahrain Rebellion Movement, Tamarod, for the main rally.
The group posted on Wednesday a call to gather at 4:00 pm (1300 GMT), near the US embassy. But a new location was announced later in the day, suggesting that tight security has thwarted any attempt to gather.
An online video statement by Hussein Youssef, who is said to be one of the founders of Tamarod and who lives abroad, called on protesters to assemble at Al-Seef junction, west of Manama.
Tamarod was formed last month, mimicking Egypt's Tamarod movement, which spearheaded the nationwide protests that triggered the army's overthrow of Islamist president Mohamed Morsi.
Bahrain's rulers have assumed sweeping new powers to crush demonstrations, but the opposition activists insisted they would go ahead with their planned protest.
On August 1, Tamarod posted an open letter asking the US embassy to provide protection for a rally at its doorstep, saying it poses "ethical responsibilities" for Washington.
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The group said the goal of the demonstration was a "real democracy in Bahrain not less than that found in Western countries such as the USA and the United Kingdom."
In Washington, Marie Harf, deputy spokeswoman at the US State Department, said she was "not going to speculate about what might or might not happen" on Wednesday.
"We support the right of individuals to peacefully assemble and of course, the right of freedom of expression, including in Bahrain, and our support for these principles has not changed, including in Bahrain."
The interior ministry said "terrorists" briefly blocked the Khalifa al-Kabeer highway, in Muharraq governorate, with burned tyres, before security forces cleared the way.
In another statement, it said an Asian fork-lift driver was injured when a "group of terrorists" hurled a petrol bomb at the vehicle while it was clearing a road blocked by protesters.
At least 80 people have been killed in Bahrain since the Arab Spring-inspired protests erupted in early 2011, according to the International Federation for Human Rights.
Veteran Prime Minister Prince Khalifa bin Salman, an uncle of King Hamad, warned on Saturday that the government would not tolerate any threat to public order.
The UN Human Rights Office has appealed to the Bahraini government to respect the right to peaceful protest.
Amnesty International urged the authorities to avoid the use of force under the "draconian" new measures, insisting the people must have the right to demonstrate peacefully.
King Hamad issued an amendment this month to the law on public gatherings, banning protests in the capital. He also decreed stiffer penalties for "terror acts."
The authorities report a growing number of shootings and bombings targeting police stations and patrols in Shiite villages outside Manama, blaming "terrorists."
Strategically located across the Gulf from Shiite Iran, Bahrain is home to the US Navy's Fifth Fleet and is an offshore financial and services centre for its oil-rich Arab neighbours in the Gulf.