A Sri Lankan minister says he has begun a hunger strike outside the UN's Colombo offices demanding that it stop its probe into alleged war crimes.
Housing Minister Wimal Weerawansa's announcement follows two days of demonstrations outside the office by protesters angry over the inquiry.
The government denies its troops committed war crimes.
But some foreign governments and international organisations say there is evidence to the contrary.
The BBC's Charles Haviland in Colombo says Mr Weerawansa is lying alone on a mattress on a bed near the main gate of the UN office.
Several Buddhist monks are also there and have given blessings to the demonstration.
Pinned to a tree nearby is a photograph of UN Secretary-General Ban Ki-moon with insulting captions stuck on it, our correspondent says.
Also pinned up are pictures of the three senior UN officials who will serve on Mr Ban's advisory panel labelled "three idiots".
"I am starting a fast till death. Only when the accusations of war crimes are withdrawn and the [UN] panel abolished, I will stop this [the fast]," Mr Weerawansa said.
One the protesters told the BBC that "Western people had done all sorts of human rights violations in the past, and now they are coming and telling us how to manage human rights".
Our correspondent says that the UN operation in Sri Lanka has been significantly disrupted by the protests, with few staff who work in the offices able to go to work.
On Tuesday the UN said it "strongly" objected to the protest at its compound, which was hindering its "vital work".
The government has pledged to ensure UN staff are able to enter and leave their workplace, but our correspondent says it is tacitly approving of Mr Weerawansa's demonstration.
Opposition parties say they fear the events will bring shame and disrepute on Sri Lanka.
The government has refused to grant visas to the UN advisory panel's three members, saying the investigation violates its sovereignty.
There have been consistent allegations that both the army - and Tamil Tiger rebels who troops routed last year - committed crimes at the end of the war.
About 7,000 civilians died in the last five months of the war, according to the UN.
It says the panel, announced last month, will report back within four months and will advise on how to deal with alleged perpetrators of abuses.
The protesters, many of them Buddhist monks, say their action will continue until the UN disbands the panel. The UN insists there are no plans to disband it.