"We view the attempt to raise war crimes charges against us as a serious crime. It will be action against our hard won peace," he said at an event marking the 66th anniversary of independence in the south western town of Kegalle.
The US has said it would table a resolution against Lanka over its human rights accountability and slow pace of reconciliation, putting new pressure on Colombo to address war crimes allegations.
The UN has already asked Lanka to punish army personnel responsible for atrocities during the civil war against the LTTE that ended in 2009. Rajapaksa said that the powerful nations failed to fully understand the challenge faced by Lanka in combating the LTTE.
"No country was bothered when the LTTE killed their own leaders and even the Indian Prime Minister Rajiv Gandhi. "No one raised rights concerns when the LTTE forcibly recruited school children. "Powerful nations are now trying to hide behind the northern people in trying to interfere in our country," he said.
Rajapaksa urged powerful nations not to be swayed by information coming from defeatist forces meaning the pro-LTTE Tamil diaspora. "Geneva (resolution) will be an attack against Sri Lanka. We will not betray our sovereignty," he said.
Sri Lanka encountered similar UN resolutions both in 2012 and 2013, moved by US and supported by India. The previous resolutions sought commitments from Sri Lanka on reconciliation and rights accountability.