Bahrain's Prime Minister Sheikh Khalifa bin Salman Al-Khalifa said protesters, who had called for his removal, would be held to account and described the anti-government unrest as a coup attempt.
"Bahrain has witnessed a coup attempt," he said in remarks carried by pro-government media on Monday. "No violators would get away with it. All co-conspirators and abettors must be held accountable."
Weeks of anti-government protests in February and March by the Shiite majority demanded more freedom, an end to discrimination and a constitutional monarchy in the Sunni-ruled country, which is a US ally and hosts it fleet.
Bahrain's rulers crushed the protests last month, deployed security forces in the capital and called in troops from Gulf neighbours Saudi Arabia and the United Arab Emirates.
The government has arrested hundreds who took part in the protests and state-owned companies have fired Shiite workers who were absent from work during a strike called for by unions.
The International Trade Union Confederation said in a statement that about 2,000 workers who took part in the protests had been fired, including 22 local trade union leaders.
"The authorities are clearly targeting and discriminating against workers due to their involvement in union activities," the trade union group said. It called for the International Labour Organisation to form a commission to probe the firings.
The opposition says the government has launched a campaign against Shiites, whether or not they had joined the protests.
"They're targeting professionals, people who stand out like famous athletes," said Mattar Ibrahim Mattar, a former parliamentarian from the main Shi'ite opposition group Wefaq.
Mattar said 29 people had been killed since the protests started including six non-Shi'ites. The six included two foreigners -- an Indian and a Bangladeshi -- and four policemen.
The unrest has spurred tensions in the world's top oil region as Sunni Gulf states including top oil exporter Saudi Arabia and Shi'ite power Iran have traded accusations of meddling in Bahraini affairs.
Government officials say the protests were backed by Iran and Hezbollah, which has denied it trained Bahraini protesters.
Mattar said police attacked on Sunday a traditional Shiite celebration marking the death of the wife of a central Shiite figure from early Islamic history, and that a Shi'ite cleric who gave a speech there had since disappeared.
"I think about 10 have been injured, but people are too afraid to go to hospitals," he said.