The UN spokesman Martin Nesirky said the United Nations had contacted the United States about reports that the US National Security Agency had cracked the UN's communications encryption system.
"I understand that the US authorities have given assurances that United Nations communications are not and will not be monitored," Nesirky told reporters.
"The inviolability of diplomatic missions, including the United Nations, has been well established in international law and therefore all members states are expected to act accordingly," Nesirky added.
The spokesman would not respond however to questions about whether the United States had listened in to UN leader Ban Ki-moon's confidential video conferences and telephone calls.
The United States is engulfed in a major international controversy over spying on allies and bodies such as the United Nations and European Union. Many of the revelations are based on NSA documents leaked by whistleblower Edward Snowden.
German news weekly Der Spiegel reported in August that the US spy agency broke the UN encryption code in mid-2012. Within about three weeks, it had decoded hundreds of confidential UN communications, the report added. The NSA, on one occasion, also allegedly caught Chinese secret services eavesdropping on the UN in 2011, it added, quoting an internal report that came from Snowden. Der Spiegel also claimed that the US agency kept tabs on the EU mission after it moved into new offices in New York in September 2012. Among documents provided by Snowden were plans of the EU's premises, which the NSA codenamed "Apalachee".
Other media reports have said the French and German missions to the United Nations were also spy targets. US officials have hit back at the claims however saying foreign intelligence agencies were also spying on US leaders.