Taking exception to Pillay's recent comments, the External Affairs Ministry said, "the United Nations can conduct an effective investigation into reports of war crimes in Sri Lanka without visiting the country".
Sri Lanka has vowed not to cooperate with the investigation and allow the UN investigators into the country.
"High Commissioner who is scheduled to leave office at the end of this month making public pronouncements to the media on an investigation which has commenced only recently is a clear indication of personal bias. It is evidence of an attempt to influence the investigation process and make it follow a preconceived trajectory," the Ministry said in a statement.
"The prejudice and lack of objectivity on issues pertaining to Sri Lanka displayed by High Commissioner Pillay in the past are unfortunate," it said.
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Sri Lanka calls the allegations against the government in Pillay's report, a flagrant violation of natural justice, which are drawn from testimonies shrouded in secrecy in view of the twenty-year confidentiality granted to those who had given the testimony, it said.
"The United Nations Human Rights Council should seek to work with Sri Lanka in a cooperative, collaborative, constructive and transparent manner to further strengthen the State's capacity to promote and protect human rights but Pillay, instead, pays scant regard to the ongoing delicate process of reconciliation in Sri Lanka argues," the statement said.
Sri Lanka has dubbed the resolution an intrusive step taken by the rights body and the appointment of the investigating panel as a breach of its sovereignty and refused to cooperate with the investigation.