Former Sri Lankan Army chief Sarath Fonseka was arrested Monday and will be court-martialled for military crimes, an official said.

Lakshman Hullugala, director general of the Media Centre for National Security, told state television that Fonseka will be court-martialled.

Fonseka has been accused of revealing military secrets and also plotting the assassination of President Mahinda Rajapaksa, the Daily Mirror of Sri Lanka reported on its website.

He was arrested by the military police.

Fonseka's media secretary Senaka de Silva was also arrested.

Fonseka was the main challenger to Rajapaksa in the country's sixth presidential election Jan 26, in which Rajapaksa defeated him by 1.8 million votes.

Fonseka was a key figure in the government's military offensive against Tamil Tiger rebels between 2006 and 2009.

He resigned from the military in November 2009 and ran for the presidency as the common candidate of the opposition parties.