The main opposition United National Party has called for an international probe.
Sri Lanka has been described as one of the most dangerous places in the world for journalists after Iraq with a string of unsolved murders of journalists.
He was announcing the capture of Elephant Pass, a narrow neck of land connecting the northern Jaffna peninsular with the rest of the island, from Tamil Tiger guerillas who are engaged in a three decade long separatist conflict.
"There are local and international conspiracies to dilute the win," President Rajapaksa said in a nation-wide television address.
"When a country is going forward without being controlled by international forces this type of conspiracies happen."
He said the ki