BERLIN — The US National Security Agency has bugged the United Nations' New York headquarters, Germany's Der Spiegel weekly said on Sunday in the latest in a series of reports on US spying that has strained relations between Washington and its allies.

Citing secret US files that the magazine has seen stemming from fugitive former intelligence contractor Edward Snowden, Der Spiegel said the revelations proved how systematically the United States spied on other states and institutions.

Der Spiegel said the documents showed that US intelligence agents bugged both other states and institutions including the European Union and the UN's Vienna-based nuclear watchdog, the International Atomic Energy Agency (IAEA).

In the summer of 2012, NSA experts succeeded in getting into the UN video conferencing system and cracking its coding system, according one of the documents cited by Der Spiegel.

"The data traffic gives us internal video teleconferences of the United Nations (yay!)," Der Spiegel quoted one document as saying, adding that within three weeks the number of decoded communications rose to 458 from 12.

Internal files also show the NSA spied on the EU delegation in New York after it moved to new rooms in autumn 2012. Among the documents copied by Snowden from NSA computers are plans of the EU mission, its IT infrastructure and servers.

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.

Snowden's leaks have embarrassed the United States by exposing the global extent of its surveillance programs. Washington has said its spies operate within the law and that the leaks have damaged national security.

British police said on Aug. 22 that documents seized from the partner of a Brazil-based American journalist who has led coverage of Snowden's leaks were "highly sensitive" and, if disclosed, could put lives at risk.

This was the latest twist in a surveillance scandal that has pitted President Barack Obama against the Kremlin over its granting of asylum to Snowden and has prompted British Prime Minister David Cameron's advisers to demand the return of NSA secrets leaked by Snowden to the Guardian newspaper.

Earlier this month, Obama announced plans to limit US government surveillance programs, saying the United States could and should be more transparent.

The issue has also become a hot topic in Germany before an election next month. Some reports have suggested that German intelligence agents have cooperated with U.S. spies.

There could be a voter backlash if it emerges that Chancellor Angela Merkel, tipped to win a third term, knew more about such cooperation than she has so far acknowledged.