MANAMA, Bahrain — Authorities detained at least six prominent opposition activists today as the crackdown on dissent widened under martial law-style rule in the tiny Gulf nation, a rights group and relatives of the arrested said.

Security forces had full control of parts of central Manama, a day after overrunning a protesters’ camp in the capital and clashing with Shiites elsewhere. At least five people were killed — two policemen and three protesters — in Wednesday’s assault on the encampment in Pearl Square, according to opposition groups and the government.

The Bahrain Youth Society for Human Rights said those taken into custody in the pre-dawn raids include Hassan Mushaima and Abdul Jalil al-Sangaece — who were among 25 Shiite activists on trial on charges of trying to overthrow the nation’s Sunni rulers.

The case was dropped in a bid to calm tensions after political unrest began last month, but the latest sweeps suggest authorities have abandoned efforts at dialogue and are trying to silence opposition leaders.

Bahrain has imposed a three-month emergency rule that gives the military wide powers to battle the pro-democracy uprising that began in mid-February in the strategic nation, which hosts the U.S. Navy’s 5th Fleet.

Increasingly, however, the struggle appears to be framed along sectarian lines: the Sunni monarchy and its backers using everything at their disposal to retain power, and Shiites hoping their overwhelming population advantage will be their most potent weapon to disrupt the country and bring the leadership to its knees.

Sunni authorities in the region also see Bahrain as an important stand against possible expansion of influence by Shiite power Iran.

Riot police fired tear gas on several dozen protesters trying to organize a march in the mostly Shiite Manama suburb of Jidhafs, which is less than a half mile from Pearl Square. As the clash unfolded, residents tried to block police vehicles with makeshift barricades including metal tables, pieces of wood and even gym weights.

The Youth Society group said the detained include Shiite activists Abdul Wahad Hussein and Hassan Hadad and Sunni liberal leader Ibrahim Sharif, who had joined with Bahrain’s majority Shiites to demand the Sunni monarchy loosen its grip on power.