Despite promises to stop spying on U.S. allies, new reporting on Tuesday revealed that the National Security Agency (NSA) under President Barack Obama continued to surveil friendly heads of state, including Israeli Prime Minister Benjamin Netanyahu.

The exclusive investigation by the Wall Street Journal revealed that Obama ramped up the surveillance of top Israeli officials late in his first term out of concern that the Middle East ally would try to derail a future nuclear agreement with Iran.

The spying continued despite the U.S. president's pledge to curb the program after documents leaked by NSA contractor Edward Snowden in 2013 showed that the United States had spied on over 100 world leaders, most notably German Chancellor Angela Merkel.

Following those revelations, a number of individuals including Merkel and French President François Hollande, were allegedly put on a list declared off-limits to U.S. eavesdropping.

Netanyahu was apparently not included on that list. One senior U.S. official was quoted by the Journal as saying, "Going dark on Bibi? Of course we wouldn’t do that."

The Obama reportedly justified the ongoing surveillance on the grounds that it served a "compelling national security purpose." According to unnamed current and former officials, the U.S. president had the support of lawmakers from both parties who believed Netanyahu would pursue a preemptive strike against Iranian nuclear facilities.

The NSA reportedly intercepted phone conversations that exposed how Israeli officials pressured U.S. lawmakers to oppose the deal and also coached American-Jewish groups on lines of arguments to use in domestic lobby efforts.

What's more, the investigation revealed how Israel's military intelligence Unit 8200 was also spying on the United States and had shared details of the U.S.-Iran negotiations with Israeli officials.