MK Shivajilingam, Member of Northern Provincial Council and a senior leader of Tamil National Alliance, in a letter to Prime Minister Modi sought India's support for an independent probe under the auspices of the United Nations.
"The Tamil people request that India changes its position of opposing the UN independent investigation on Sri Lanka, and supports such investigation which is our only hope for justice, accountability and protection.
In the letter, a copy of which was circulated to the media, he flagged six issues for Modi's attention.
Last month, Northern Provincial Council through a resolution had urged the UN High Commissioner for Human Rights to probe allegations of what it called genocide, a month after Maithiripala Sirisena assumed office as Sri Lanka's new president.
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However, this was denounced as a "radical position that would scuttle reconciliation" by the Lankan regime.
Against this backdrop, Shivajilingam wrote to Modi seeking a shift in India's stand.
He said the 2002 Oslo Declaration which envisaged a federal structure was welcomed by the international community.
Welcoming Modi to Sri Lanka on his maiden visit - the first by an Indian Prime Minister in 28 years after Rajiv Gandhi's tour of the country in 1987 - he said the Lankan government should be persuaded to demilitarise the North East region and return the lands seized from the Tamils.
"Provide help to release Tamil political prisoners, those surrendered, imprisoned, and disappeared during the end of the war," he said.
Besides resolving issues faced by fishermen of both the countries, Shivajilingam sought restoration of ferry service between Thalaimannar and Rameswaram, and air-link from Tamil Nadu to Plalaly and Trincomalee.