A series of bomb blasts in Bahrain's capital killed two people Monday, authorities said, a sign that some factions within the opposition may be increasingly turning to violence in the nearly 21-month uprising against the Gulf nation's Western-backed rulers.

The apparently coordinated string of five explosions in Manama — described by officials as "terrorism" — comes less than a week after Bahrain banned all protest gatherings in attempts to quell the deepening unrest in the strategic kingdom, which is home the U.S. Navy's 5th Fleet.

Clashes have not eased, including crowds pelting three police stations with firebombs early Sunday. More than 55 people have been killed Bahrain's unrest since February 2011 as the nation's majority Shiites press for a greater political voice in the Sunni-ruled island nation.

Officials also suggested three could be crackdowns against Shiite religious leaders, and that could sharply intensify the clashes. Government spokeswoman Sameera Rajab blamed the attacks on statements by some Shiite "religious figures who haven't ceased inciting violence against civilians and police."

She said authorities would show "zero tolerance" in its efforts to stamp out unrest.

In Monday's violence, two Asian men were killed and a third person was injured as at least five homemade explosive devices were detonated, the Interior Ministry said. One man died after kicking a bomb and triggered an explosion, and the other died from injuries in a separate blast, officials said. The dead were a 29-year-old Indian and a 33-year-old citizen of Bangladesh, they said. A 33-year-old Indian was wounded.

Like all Gulf Arab countries, Bahrain has a large South Asian community of expatriate workers.

The official Bahrain News Agency described the blasts, over a nearly five-hour span, as an "act of terrorism."

Anti-government factions in Bahrain have used homemade bombs in the past, including a blast that killed a policeman last month in a mostly Shiite village. The latest attack suggests an expanding campaign of violence because of the scope of the bombings and their placement scattered throughout the heart of the capital, including near one area of restaurants and nightlife popular with Westerners.

On Wednesday, foreign ministers from the Gulf Cooperation Council plan to meet in Bahrain to discuss regional issues, including Bahrain's tensions and growing clashes in Kuwait between security forces and an opposition led by Islamists.

Bahrain's Western allies have urged renewed efforts at dialogue to ease the crisis, but opposition groups insist that talks cannot move forward unless the monarchy is willing to make greater concessions to loosen its hold on the country's affairs. Bahrain's leaders have so far made reforms that include transferring more oversight powers to the elected parliament.

Shiites make up about 70 percent of Bahrain's 525,000 citizens. They claim they face systematic discrimination, such as being blocked from top political and security posts.

Last week, the U.S. State Department issued unusually harsh criticism against ally Bahrain after its decision to outlaw public demonstrations. Previously, officials in Bahrain had permitted some protest marches, but most clashes have occurred outside the authorized rallies.

"The decision to curb these rights is contrary to Bahrain's professed commitment to reform and will not help advance national reconciliation nor build trust among all parties," said State Department spokesman Mark Toner.