The UN said Wednesday that "the US authorities have given assurances that United Nations communications are not and will not be monitored".
UN spokesman Martin Nesirky made the remarks at a daily news briefing here, Xinhua reported.
Asked about reports of past intelligence gathering activities by the US National Security Agency (NSA), Nesirky said "in August, when these reports first surfaced, the United Nations had said it would be in touch with the relevant authorities".
"The (UN) Secretariat was indeed in touch with the US authorities," he said.
"The inviolability of diplomatic missions, including the United Nations, has been well established in international law. Therefore all member states are expected to act accordingly," said the spokesman.
The White House has faced criticism for the NSA's surveillance practices since the first revelations by a former agency contractor Edward J. Snowden, in June.
However, in recent weeks, the US government has struggled to quell a new diplomatic storm over reports that the American agency had monitored the cellphone of German Chancellor Angela Merkel for more than a decade. Brazil, France and Spain also voiced their outrage over US spying on their leaders.
