Bahraini Interior Ministry on Tuesday claimed bomb blasts detonated Monday, killing two Asian street cleaners, were homemade and described the blasts as "terrorist acts" - its term for violence by opposition activists.
But an opposition politician and a rights activist said the attacks, which came days after the government said it had banned all rallies and opposition gatherings to ensure public safety, could have been the work of government forces trying to justify the ban or a further crackdown.
Injuries to protesters or police are relatively common in the 21-month-old uprising, but attacks on the public have been rare on the Gulf island, where the Sunni Muslim Al Khalifa dynasty rules over a majority Shi'ite population.
The explosions took place between 4:30 and 9:30 a.m. (0130-0630 GMT) in the Qudaibiya and Adliya districts of Manama, the official Bahrain News Agency (BNA) said, citing a police official. It described the explosives as "locally made bombs" and said a third Asian worker had been wounded.
One of the attacks took place outside a cinema, where one of the street cleaners died when he kicked a package that blew up. A witness said that blast caused little material damage, suggesting it had not been large.
Attacks on police
Police say they have been the target of numerous attacks with homemade bombs since April, including one that killed a policeman last month, as the government has stepped up efforts to quell an uprising that has crippled the economy.
The United States condemned the attack and called for all sides to enter into a dialogue without pre-conditions to resolve the tension.
"We remain deeply concerned about the rise of tensions in Bahrain... all of this just undercuts the process of national reconciliation that we have strongly been urging on Bahrainis of all stripes for many, many months," State Department spokeswoman Victoria Nuland said in Washington.
Opposition politician Matar Matar of the Shi'ite party Wefaq said he doubted that opposition activists were behind Monday's attacks, noting that leading Shi'ite clerics had called on followers to avoid escalating the conflict with the government.
He suggested the police or military might have been responsible, or a rogue unit.
"This incident is strange - why would anyone target workers?" he said. "I'm worried that police and military are losing control of their units or it is (preparation) before declaring martial law."
Maryam al-Khawaja, acting head of the Bahrain Centre for Human Rights, said: "As always, we condemn violence but, given the Bahraini authorities' background in spreading disinformation, we call for an independent investigation into the deaths of the two migrant workers."
Khawaja, who is based in Denmark, said the attacks were "not grounds to start a campaign of collective punishment, arbitrary arrests, and torture, as we've see happen before".
Amnesty International called for an independent investigation into the attacks. "...those responsible (must be) brought to justice in proceedings that comply with internationally recognised standards for fair trial and with no possibility of the death penalty," a statement said.
Shi'ites complain of discrimination in the electoral system, jobs, housing and education, and say they are mistreated by government departments, the police and the army. Government promises of action to address their concerns have come to nothing, they say. The authorities deny this.
Washington has urged Bahrain to begin dialogue on democratic reforms with the opposition. But its criticism has been offset by its support for a country that plays a key role in US efforts to challenge Iranian influence in the region and hosts the US Fifth Fleet, which patrols oil-shipping lanes.
Bahrain has become caught up in regional rivalry between Sunni states such as Saudi Arabia - which helped Bahrain to crush mass protests last year - and Shi'ite power Iran, which champions the cause of Bahrain's Shi'ite opposition but denies accusations of fomenting the unrest.
Thirty-five people were killed in Bahrain during protests in February and March 2011 and the two months of martial law that followed. While mass protests in central Manama have been stamped out, there are still clashes between protesters and riot police almost every day in Shi'ite districts.
Activists and rights groups say nearly 50 civilians have been killed in the turmoil since the end of martial law, while the authorities say two policemen have died.