Lashing out at critics, Sri Lankan President Maithripala Sirisena on Saturday said his government was "determined and dedicated" to achieve national reconciliation with the minority Tamils despite the work of some opportunists.

Sirisena made the remarks while addressing the 69th anniversary of Lanka's independence celebrations here.

"We are determined and dedicated in our commitment despite the work of some opportunists. The government would work towards a knowledge and innovation based economy," he said, blaming them for their aiming of narrow political gains.

Succeeding Mahinda Rajapaksa, President Sirisena's unity government had set in a series of reconciliation measures.

The government has promised a new constitution to address the Tamil political aspirations. Tamils say the progress had been painfully slow and questions the government's commitment despite making some symbolic gestures to win over them.

Sirisena's work to hand back Tamils the land held for military purposes and release some of the former terrorist suspects have raised criticism from Rajapaksa's joint opposition who claim that Sirisena was appeasing the Tamils and putting the country's national security at risk.

While the national ceremony was happening here, a section of the hardline Tamils held a demonstration in the Northern capital of Jaffna.

"The independence day is our black day. The Tamil community is in grief," said MK Shivajilingam a Northern provincial councilor who led a protest of several hundreds.

"Our land issues, detention of our people and disappearances have not been addressed. We want an international investigations on crimes against Tamils," Shivajilingam said.

According to the UN figures, up to 40,000 civilians were killed by the security forces during Rajapaksa's regime that brought an end to nearly three-decades long civil war in Sri Lanka with the defeat of LTTE in 2009.