The Sri Lankan government has sought two more years from the UN Human Rights Council to deliver on the accountability mechanism.
Wigneswaran said "the UN must see first what good the government has done so far".
"Without doing that and granting time for some political reason does not see correct to me," the Tamil leader said.
The northern and eastern parts of Sri Lanka are the traditional homeland of the ethnic Tamil people where an almost three-decade-long separatist war was fought by the LTTE which ended in 2009 during the tenure of former president Mahinda Rajapaksa.
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"Allowing the missing persons' protest for 28 days was wrong. The report on the missing has not been published so far. The government is in the mentality of safeguarding the military men linked to the disappearances," Wigneswaran said.
The northern provincial council last week had resolved that the government had not taken adequate measures to fully implement the Resolution 30/1 that it co-sponsored at the UNHRC Session in September 2015, especially with regard to the accountability, establishment of a Commission for truth, reconciliation; nonrecurrence of oppression, return of lands to its rightful civilian owners and an office of reparation.
Earlier this month, the UNHRC had criticised Sri Lanka's "slow" progress in addressing its wartime past and reiterated its earlier call for hybrid court of international and local judges to investigate allegations of rights violations.
The Tamils insist on having foreign judges and investigators claiming lack of confidence in the local judiciary.
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