Bahraini security forces used tear gas and stun grenades to disperse hundreds of opposition supporters attempting to protest alongside a highway leading to the island kingdom's capital Thursday.
The clashes follow 10 months of unrest between Bahrain's Sunni monarchy and an opposition movement led by the country's majority Shiites. They came during a visit by the U.S. State Department's top human rights envoy, who expressed concern about the government's use of tear gas and other tough tactics against protesters.
Thursday's clashes erupted near the town of Diraz and other opposition stronghold villages west of the capital, Manama. Riot police were seen chasing protesters away from entrances to the key highway and back into the largely Shiite communities that line the road.
Online activists have issued calls on Twitter and other social media for protesters to occupy the highway, seeking to maintain momentum for protests in the strategically important Gulf nation that hosts the U.S. Navy's 5th Fleet.
Hundreds of protesters, some waving red and white Bahraini flags, were seen along the side of the highway when the clashes broke out in the afternoon.
Witnesses described a heavy police presence in the area ahead of the protest, with security forces dressed in riot gear and helicopters hovering low overhead.
The highway connects a string of largely Shiite villages west of Manama. It leads to a junction that is roughly half a kilometer (a quarter of a mile) south of Manama's Pearl Square, where this year's uprising originated. Government forces evicted protesters and tore down the pearl sculpture that marked the site in March.
The now heavily guarded square holds great symbolic value for the opposition movement, and protesters have repeatedly tried to retake it.
The clashes erupted during a visit by U.S. Assistant Secretary of State Michael Posner, head of the Bureau of Democracy, Human Rights and Labor.
In prepared remarks to reporters, he praised the king for taking steps to implement reforms recommended in a report last month that outlined human rights abuses carried out by the government. He called on both the government and protesters to refrain from violence.
Posner urged the government to do more.
He cited "the need for tangible action on several urgent issues," including reinstating workers unfairly dismissed from their jobs. He also raised concerns about court cases involving doctors and others that he said appear to be based at least in part on their criticism of the government, as well as proposed media laws that could stifle political debate.
Washington also remains concerned about the government's "excessive use of force, including tear gas, in response to ongoing street protests," he said.
More than 35 people have died in clashes and protest-related violence since February, inspired by other Arab Spring revolts. Bahrain's protests are the largest and most sustained to have hit the Arab monarchies and sheikdoms that line the Persian Gulf.