Sri Lanka's Supreme Court on Thursday unanimously ruled that the dissolution of Parliament by Maithripala Sirisena was "unconstitutional", in a major setback to the embattled President, whose controversial decisions plunged the island nation into an unprecedented constitutional crisis.

A seven-member apex court bench said that the President cannot dissolve Parliament till it completes its a four-and-half-year term. The decision has laid to rest one of the many controversial moves which had complicated the constitutional crisis emanating from President Sirisena's decision on October 26 to sack the incumbent prime minister, Ranil Wickremesinghe, and install former president Mahinda Rajapaksa in his place. He also dissolved the 225-member Parliament and called for a snap election on January 5.