Germany's Der Spiegel claims to have analyzed secret NSA documents that show that, last summer, the US intelligence agency managed to get access to the video conferencing system used at the United Nations headquarters in New York, leading to "a dramatic improvement of data on video conferencing and our ability to decode that data," according to the document.

The NSA also allegedly caught Chinese intelligence spying on the UN and started analyzing the material China was wiretapping.

The alleged spying activities are illegal. The US has a long-standing agreement with the UN stipulating that the US refrain from covert operations with regards to the UN's activities.

Der Spiegel also claims that the NSA documents it has analyzed show that the NSA spied on the EU even after its move to its new UN embassy in September 2012.

The article says the NSA's nickname for the EU embassy was "apalachee," the EU embassy in Washington was dubbed "magothy."

The NSA used traditional bugging devices to spy on UN activities, says the report. It also allegedly copied hard drives and infiltrated computer networks in Washington.

Der Spiegel also says that the NSA operated a global monitoring network called "Special Collection Service" in more than 80 embassies and consulates, often without the host country's knowledge.

The NSA documents urged staff to keep the network a secret so as not to damage relations with other countries.