President says he will even 'sit on electric chair on behalf of the country'

"All these days we did not demonstrate our strength, but now on May Day we will show our strength," the president is quoted as saying by the AFP news agency.

He made the comments on Saturday addressing his party officials.

The UN report apparently alleges that his government committed war crimes and crimes against humanity in the final stage of the conflict against Tamil rebels, which ended two years ago.

In the strongly worded report, the panel found credible allegations, it says, that the Sri Lankan government killed civilians by shelling, on a large scale, areas where it had encouraged people to go.

It systematically shelled hospitals on the frontlines, it says, and deprived people inside the conflict zone of food and medical supplies.

Minister Wimal Weerawansa earlier held a 'fast unto death' protest in front of the UN office seeking the withdrawal of the panel

President Rajapaksa, who dismisses the allegations, suggested that May Day rallies be used to show public support for the Sri Lankan government.

"On behalf of the country, if they ask me to sit on the electric chair, I will happily do it," Mr Rajapaksa said.

The report also criticises the way in which people who fled the conflict zone were kept in closed camps, in conditions it describes as "terrible."

If proven, it says, some of these allegations would amount to war crimes and crimes against humanity.

The Sri Lankan government has already rejected the report, describing it as fundamentally flawed.

The UN report has not been released but a Sri Lankan newspaper published what it said was a summary of its findings.