Wickremesinghe said his government could only act within the framework of the Sri Lankan Constitution, which does not allow foreign judges to operate in the country.
He, however, said that international expertise would be welcomed but the country's judiciary would have to approve the extent of their involvement.
The Sri Lankan Premier's assertions came in the backdrop of UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein call for a hybrid special court, integrating international judges, prosecutors, lawyers and investigators to probe the alleged rights abuses during the civil war that ended in 2009.
Sri Lanka has been consistently insisting on a domestic mechanism to investigate the matter.
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Rights groups claim that the Sri Lankan military killed 40,000 civilians in the final months of the three decade-long brutal ethnic conflict.
Addressing reporters, Wickremesinghe said his Foreign Minister Mangala Samaraweera would be having talks with the UNHRC to apprise them of the local constitutional impediments.
Sri Lanka is averse to an international probe as it tends to cause displeasure among the Sinhala majority, who are opposed to military officials being tried for war crimes in combating the separatists Liberation Tigers of Tamil Eelam.
Wickremesinghe said he and his government had saved both the Rajapaksas from facing an international war crimes inquiry by "properly handling" the issue since January.
It was Rajapaksa's blunder that forced Sri Lanka to subject it to an international inquiry, said Wickremesinghe.