By Shihar Aneez
COLOMBO (Reuters) - Political parties mainly representing Sri Lanka's minority Tamils and Muslims, who account for a quarter of the total vote, have said they will back President Mahinda Rajapaksa's challenger in a Jan. 8 presidential poll.
Tamil National Alliance (TNA), former political proxy of the defeated Tamil Tiger rebels, said in a statement on Tuesday "the values of democracy, good governance, and rule of law have suffered unprecedented assault" under Rajapaksa.
The 69-year-old leader has denied opposition allegations of corruption, nepotism and intervention in the judiciary. He also promised speedy reconciliation after ending a 26-year war against Tamil Tiger separatists in 2009 - a pledge the Tamil group said he had broken.
"Instead of pursuing reconciliation, the Rajapaksa regime has permitted extremist groups to carry out attacks against minority peoples and their places of religious worship," it said.
Rajapaksa was expected to win easily when he announced the poll last month. But 23 of his party legislators in a 225-member parliament have defected since then to join his challenger, former Health Minister Mithripala Sirisena, who has promised good governance, democracy, and an end to corruption.
Two opposition legislators have joined Rajapaksa this month.
On Sunday, the main Muslim party with eight legislators left Rajapaksa's United People's Freedom alliance to join Sirisena's campaign after Muslims faced a series of attacks by Buddhist extremist groups since early 2012.
Rajapaksa won elections in 2005 and 2010 with a majority of Sinhala Buddhists backing him and minimum support from minorities.
He is still backed by two Tamil parties and some fringe Muslim parties, but his core rural Sinhala Buddhist voters are now being offered concessions and subsidies by Sirisena.
(Editing by Dominic Evans)