Sri Lanka on Saturday rejected UN human rights chief Zeid Ra'ad al-Hussein's condemnation of the government's persistent efforts to discredit the UN inquiry into mass atrocities on the island, accusing him of challenging the right of a sovereign state to "raise concerns regarding procedural aspects of an investigation".

"The Government of Sri Lanka, its departments and agencies made no attempt whatsoever to prevent bona fide witnesses from submitting information to the investigation team," Colombo's ambassador to the UN in Geneva, Ravinatha Aryasinha, said in a statement.

"Neither was any attempt made to deter and intimidate individuals from submitting evidence. The submissions that the Investigation would have received by now would stand to prove this fact," he said.

"[You] have challenged the right of a sovereign State to raise concerns regarding procedural aspects of an Investigation which impacts its people and their future in the context of the ongoing sensitive reconciliation process."

Ariyasinha said the government will not submit its people to an unfair investigation and expressed concern about the "intemperate language" used by the human rights chief to "attack and vilify a sovereign member of the UN".

"The Government of Sri Lanka has steadfastly maintained that it owes to the country’s dignity not to subject its people to an investigation that does not conform to even the minimum requisites of justice and fairplay. This position has been overwhelmingly endorsed by the national Parliament. It is a principled position which the Government chose to take that was supported by many countries in the Council."

"It is a matter of deep concern to note that you, as a high official of the UN system, have resorted to the use of intemperate language to attack and vilify a sovereign member of the United Nations."

"Further, you have chosen to cast aspersions and denigrate a democratically elected Government. In fact, some countries have, on extremely cogent grounds, rejected mandates of the Council previously in much stronger ways, and have not been censured in the manner as in this instance.

"This undoubtedly confirms the double standards being applied. This type of action on your part would regrettably constrain constructive engagement which the Government of Sri Lanka has consistently sought to pursue," Ariyasinha said.