COLOMBO (Reuters) - Sri Lankan Health Minister Mithripala Sirisena resigned on Friday and said he would run as an opposition candidate against President Mahinda Rajapaksa in a snap election in January.
The challenge from within his own ranks will be a blow for Rajapaksa, who is seeking an unprecedented third term and remains a popular leader despite foreign criticism over his sweeping powers and human rights record.
"One family has taken control of the economy, power and the party," Sirisena said. "The country is moving toward a dictatorship."
Sirisena, who is also the general secretary of Sri Lanka Freedom Party (SLFP) headed by Rajapaksa, defected a day after the president announced a poll in January despite a request from allies not to go for an early election.
The Election Commission said on Friday the election will be held on Jan. 8.
The fisheries minister and three other lawmakers also resigned from their positions, pledging support for Sirisena. Separately, two legislators of the ruling coalition have joined the opposition since Thursday.
The main opposition United National Party (UNP) along with many Rajapaksa rivals have thrown their weight behind Sirisena as their common candidate for the presidency.
The defections will split Rajapaksa's main vote base of Sinhala Buddhists, who account for around 70 percent of the population. Strong opposition to Rajapaksa from some prominent Buddhist monks will also stand in his way.
Rajapaksa's poll ratings have fallen sharply, and critics, including his coalition partners, say Sri Lanka's "executive presidency" - introduced by a 1978 constitution - gives him and his family excessive power.
"I will abolish the executive presidency in 100 days. I will definitely win in the next presidential election," Sirisena said. "My government will ensure press freedom. More ministers will join me in the future."
Former president Chandrika Bandaranaike Kumaratunga, who is also backing Sirisena, said the defectors' lives were now in danger.
"A situation has been created where no one can criticize the current administration," Kumaratunga told reporters.
It was the first time since his election that Rajapaksa has faced such heavy criticism in public from his own party members.
Rajapaksa, 69, came to power in 2005 and retained the presidency in 2010 on a wave of popularity after the military defeated Tamil Tiger separatists in 2009, ending a 26-year-old civil war on the Indian Ocean island state.
He has been tainted by accusations of nepotism, although he has responded by saying that any relatives in parliament are there because people elected them and not because he chose them.
Reporting by Ranga Sirilal, Writing by Shihar Aneez,; Editing by Angus MacSwan