Sirisena, who in a stunning upset defeated strongman Mahinda Rajapaksa in the polls last year, said he was satisfied with the reforms he introduced over the past year to achieve national reconciliation, including with minority Tamils.
"We must not leave room for extremists both in the south and north. We have to make sure there will not be another war in this country," Sirisena said.
Sirisena handed a shock defeat to Rajapaksa, having come forward as the opposition challenger after breaking ranks with the two time president.
Sirisena, since coming to power, has reduced his presidential powers and strengthened key areas of governance by setting up independent commissions on police, judiciary elections and public service.
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"We have physically ended the war but were not able to identify and address root causes of the war," Sirisena said referring to military victory over the LTTE in 2009 that ended the nearly three decades-long civil war in the country.
His predecessor Rajapaksa had antagonised both Tamil and Muslim minorities in order to appease the Sinhala majority.
Sirisena is to address the parliament tomorrow launching his constitutional reform programme to draft a brand new statute.
"Some accuse us of leaving room for a division of the country and of endangering national security through the new Constitution. We will do neither," he said.
The keynote address at the function marking the anniversary was delivered by Gopalakrishna Gandhi, a former Indian High Commissioner to Sri Lanka.