Sirisena issued the notice midnight Friday announcing the election for the 225-member Parliament for Aug. 17.
Sirisena won the January presidential election against Mahinda Rajapaksa on a pledge of full-scale political reforms, but has faced resistance from lawmakers in implementing his program. It includes reducing powers of the presidency and changes to the electoral system.
Majority of the lawmakers of the dissolved parliament belonged to the United People's Freedom Alliance, which Rajapaksa led until his defeat.
Sirisena is also keen to secure cooperation of a new parliament ahead of an internal investigation into war crimes allegations in the final stages of the country's civil war.
In March, Sirisena secured postponement of a United Nations report on the alleged atrocities by promising a domestic investigation. The U.N. High Commissioner for Human Rights is expected to release the report in September.
Calling an election ahead of the report is also an apparent bid to deny Rajapaksa an opportunity to come back to power by stirring up nationalism.
Rajapaksa is still popular with the country's majority Sinhalese, who oppose international involvement in Sri Lanka. He is also considered a war hero among Sinhalese for ending a three-decade civil war in 2009.
The conflict ended after government troops crushed the separatist Tamil Tiger rebels, who fought for a separate state for the ethnic minority Tamils.
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