"We will not betray you to the world," Rajapakse told troops during a colourful military parade at Colombo's seafront Galle Face promenade to commemorate the war success.
Colombo is under pressure from the West, the United Nations and international rights groups to submit to a probe into alleged war crimes committed during the final stages of the war in 2009.
The United States has warned that Colombo's failure to credibly investigate the allegations and establish genuine reconciliation with its ethnic Tamil minority could lead to an international war crimes probe being imposed.
However, Sri Lanka has the backing of China and Russia at the UN security council to thwart a possible international inquiry.
A report by a panel of experts appointed by UN chief Ban Ki-moon said last month that there were "credible allegations" that both the Sri Lankan army and Tamil Tiger rebels had been guilty of war crimes or crimes against humanity.
Sri Lanka has reacted furiously to the claim and has