The United Nations said on Monday it plans to contact the United States over a report that the U.S. National Security Agency bugged its New York headquarters and warned that countries are expected to respect the world body's diplomatic inviolability.

Citing secret U.S. documents obtained by fugitive former intelligence contractor Edward Snowden, Germany's Der Spiegel reported on Sunday that the United States succeeded in gaining access to the internal U.N. video conferencing system in 2012.

"We're aware of the reports and we intend to be in touch with the relevant authorities on this," U.N. spokesman Farhan Haq told reporters.

He said well established international law, like the 1961 Vienna Convention governing diplomatic relations, protected functions of the United Nations, diplomatic missions and other international organizations.

"Therefore member states are expected to act accordingly to protect the inviolability of diplomatic missions," Haq said.

Der Spiegel also said the European Union and the U.N.'s Vienna-based nuclear watchdog, the International Atomic Energy Agency (IAEA), were among those targeted by U.S. intelligence.

According to the documents, the NSA runs a bugging program in more than 80 embassies and consulates worldwide called "Special Collection Service".

"The surveillance is intensive and well organized and has little or nothing to do with warding off terrorists," wrote Der Spiegel.