Police clashed with protesters in Bahrain's Manama on Wednesday, arresting at least 20 people, according to the Associated Press.
Reuters said security forces resorted to tear gas and fired bird shot in a bid to disrupt demonstrations, which have been intermittant but ongoing in Bahrain for months.
The Gulf kingdom, a key ally of the United States, is a Sunni monarchy with a Shiite majority.
The unrest there is seen as part of a political groundswell that gave rise to the overthrow of longtime leaders in Tunisia and Libya several years ago.
In Manama, protesters took their frustrations to wealthy areas of the city, said the AP, some even calling on shop-owners to stop work and join a labor strike in solidarity.
Bahrain's authorities had warned they would "forecefully confront" the marches planned for Wednesday, which was also the 42nd anniversary of the island kingdom's freedom from British rule, said the AP.
Many see developments in Bahrain as part of a greater struggle for power between regional heavyweights like Iran and Saudi Arabia, a fight from which Bahrain's opposition has sought to distance itself.
The Manama-based Bahrain Center for Human Rights said "large amounts of tear gas [were] used to disperse anyone gathering on the streets," according to Al Jazeera.
"We don't care if they fire tear gas," protester Fatma Jaber told the AP. "We are used to it. We are proud that we have succeeded in shutting down the country."