The UN secretary-general has recalled his envoy to Sri Lanka and is closing an office in Colombo because of "unruly protests" over a war crimes panel.
Ban Ki-moon said it was "unacceptable" that Sri Lankan authorities had failed to prevent the disruption of the work of UN personnel in the country.
The demonstrations are being led by the Housing Minister, Wimal Weerawansa.
He has urged "progressive nations" to halt a UN probe over possible war crimes during Sri Lanka's civil war.
Mr Weerawansa, an ally of President Mahinda Rajapaksa, said he had also begun a hunger strike in a bid to increase pressure on the UN.
"I am starting a fast till death. Only when the accusations of war crimes are withdrawn and the panel abolished, will I stop this."
In a statement, Mr Ban's spokesman said he found it unacceptable that the Sri Lankan authorities had failed to prevent the disruption of the normal functioning of the UN offices in Colombo "as a result of unruly protests organised and led by a cabinet minister".
"In light of the evolving situation, he is recalling the United Nations Resident Co-ordinator, Neil Buhne, to New York for consultations. He has also decided that the UN Development Programme Regional Centre in Colombo will be closed."
"The secretary-general calls upon the government of Sri Lanka to live up to its responsibilities towards the United Nations as host country, so as to ensure continuation of the vital work of the organisation to assist the people of Sri Lanka without any further hindrance," it added.
Mr Ban named a three-member panel last month to advise on "accountability issues" arising from the final stages of the 25-year conflict between government forces and the separatist Tamil Tigers, which ended in May 2009.
About 7,000 civilians died in the last five months of fighting, according to the UN.
Some foreign governments and international organisations say there is evidence that war crimes were committed by both sides and want a UN investigation.
Sri Lanka's government denies its troops acted in contravention of international law, and considers the panel a violation of its sovereignty and an application of double standards by the West.
It has refused to grant visas to the panel's members and correspondents say it is tacitly supporting Mr Weerawansa.