Sri Lanka's new president pledged his support for the military as he marked six years since the end of the civil war on Tuesday, a day after his predecessor accused him of forgetting the country's "war heroes".

Maithripala Sirisena pledged to ensure that the Tamil Tigers, who waged a violent 37-year campaign for a separate homeland on the island, never raised their heads again as he attended a military parade to commemorate fallen soldiers.

Sirisena took power in Sri Lanka in January after winning an election against the country's strongman former leader Mahinda Rajapakse, who oversaw the military crushing of the Tamil Tiger rebels in 2006.

He has pledged to bring about reconciliation with the island's Tamil minority, who have long faced discrimination, but also needs the support of the Sinhalese majority ahead of parliamentary elections expected to be held later this year.

"I assure you that I will make every effort to ensure national security," Sirisena said during commemorations Tuesday -- previously known as "Victory Day" but now renamed "Armed Forces Day".

"I will not allow the brutal LTTE (Liberation Tigers of Tamil Eelam) terrorism to raise its head ever again.

"I have the fullest confidence in you (the troops) to safeguard the security of our motherland," he said, accusing his rivals of peddling "false propaganda" against the government.

Rajapakse, who is reported to be seeking a political comeback, had earlier accused the government of forgetting the country's "war heroes", citing the more low-key commemorations under Sirisena.

Sirisena served in Rajapakse's cabinet before quitting to stand against his one-time mentor, who had until then been regarded as odds-on for a third term.

On Tuesday Sirisena, who has lifted a Rajapakse-era ban on Tamils publicly commemorating their war dead, said the previous government had failed to achieve post-war reconciliation.

"We were all happy when the war ended. But can we be happy with the developments post war?" he said as he received a 21-gun salute at a parade involving more than 7,000 troops and police.

"We were not able to win hearts and minds of people. The true reconciliation could only be achieved by winning hearts and minds."