The four-day visit of UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein is significant following a UN Human Rights Council (UNHRC) resolution last October which mandated an investigation into alleged human rights abuses during the final phase of Sri Lanka's ethnic conflict that ended in 2009.
Hussein, on his first visit to Sri Lanka after succeeding Navi Pillay as UN rights chief, said he hoped for "constructive discussions" with President Maithripala Sirisena.
In a hard hitting report at the UNHRC, Hussein had criticised Sri Lanka's failure to deliver justice to the victims of the conflict.
He had prescribed an international "hybrid court" with foreign judges, prosecutors and investigators.
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However the current Sirisena government, which has a softer attitude towards the minority communities than the nationalist hawkish regime of former president Mahinda Rajapaksa, has cited constitutional difficulties in allowing foreign judges to operate in the island.
But Sirisena agreed to a domestic probe on allegations that 40,000 people were killed in the last phase of the war between government troops and the LTTE rebels.
In Jaffna, Tamil rights groups have organised a demonstration to highlight the plight of relatives of disappeared persons of the 37-year civil war that killed an estimated 100,000 people.
While in Colombo, the Sinhala majority nationalist National Freedom Front was to protest Hussein's visit claiming that it would lead to concessions being granted to Tamils through a political deal eventually leading to the separation of the country's Tamil-dominated north and east.