Israel spied on talks the U.S. and its allies are having with Iran over the Islamic Republic’s nuclear program, The Wall Street Journal reported.

Espionage among friends is not exactly new. In fact, the newspaper reported that the White House discovered the operation when U.S. intelligence agencies “spying on Israel intercepted communications among Israeli officials that carried details the U.S. believed could have come only from access to the confidential talks.”

The US has accused Israel of spying on international negotiations over Iran’s nuclear programme and using the intelligence gathered to persuade Congress to undermine the talks, according to a report on Tuesday.

The Wall Street Journal cited senior administration officials as saying the Israeli espionage operation began soon after the US opened up a secret channel of communications with Tehran in 2012, aimed at resolving the decade-long standoff over Iran’s nuclear aspirations.

The apparent decision by the White House to leak the allegations is the latest symptom of the growing gulf between Barack Obama’s administration and Binyamin Netanyahu’s government over the Iran talks, in which the Israeli leader suspects US officials of being ready to make too many concessions at the expense of Israeli security. Intelligence analysts suggested that the leak reflects the degree of anger in Washington at Netanyahu’s actions, and could mark a more serious blow to the already tottering relationship.

The leak has come exactly a week before a deadline for the US-Iranian negotiations in Lausanne to produce a framework agreement.

According to the report, the US has long been aware that Israel is among the shortlist of countries with the most aggressive intelligence operations targeting America, alongside Russia, China and France. It said American diplomats attending the talks in Austria and Switzerland were briefed by US counterintelligence officials about the threat of Israeli eavesdropping. It also raised the possibility that Israel gathered intelligence about the US position by spying on other participants in the negotiations, from western Europe, Russia, China or Iran. US intelligence had previously provided help to the Israelis to spy on the Iranians, the report said.

The US also conducts intelligence operations against Israel, and learned of the Israeli spying operation when it intercepted communication between Israeli officials exchanging classified information that US intelligence believed could only have been acquired by espionage.

The spying operation was part of a broader campaign by Israeli Prime Minister Benjamin Netanyahu’s government to penetrate the negotiations and then help build a case against the emerging terms of the deal, current and former U.S. officials said. In addition to eavesdropping, Israel acquired information from confidential U.S. briefings, informants and diplomatic contacts in Europe, the officials said.

The espionage didn’t upset the White House as much as Israel’s sharing of inside information with U.S. lawmakers and others to drain support from a high-stakes deal intended to limit Iran’s nuclear program, current and former officials said.

“It is one thing for the U.S. and Israel to spy on each other. It is another thing for Israel to steal U.S. secrets and play them back to U.S. legislators to undermine U.S. diplomacy,” said a senior U.S. official briefed on the matter.