The private meetings in question took place last year and involved the UK, Germany, France, China and Russia. The aim was to persuade Iran to curtail its nuclear programme in return for a lifting of crippling economic sanctions placed on the country.
Tehran has consistently said its nuclear enrichment is entirely for peaceful purposes, but other nations are concerned it may be trying to build a nuclear weapon.
Israel and the US share this worry, but a division of opinion has become apparent in terms of the extent to which Iran should have to reduce its nuclear activities – earlier this month US President Barack Obama proposed a 10-year freeze, but Israeli Prime Minister Benjamin Netanyahu reacted by saying this would not stop the development of an atomic bomb.
“I have a moral obligation to speak up in the face of these dangers while there is still time to avert them,” Netanyahu said during a speech to supporters at the time.
The end-of-the-month deadline for an agreement is approaching fast, and the latest accusation reflects escalating tensions between the two allies on the matter. Here's what each says happened, or didn't happen.
What the US Says
Last night, the Wall Street Journal published a report saying the White House had uncovered a spying operation by Israel, involving eavesdropping and the acquisition of information from confidential US briefings.
It said the discovery was made when US intelligence agencies intercepted messages shared between Israeli officials, since they contained information that could only have come from the private talks on Iran.
The US had a particular complaint about how the information was manipulated – the WSJ said the Israeli government had used the confidential information to try and bring down support for the developing deal among US lawmakers.
"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," one US official told the paper.
“People feel personally sold out,” another said. “That’s where the Israelis really better be careful because a lot of these people will not only be around for this administration but possibly the next one as well.”
What Israel says
This morning, Israeli officials denied the allegations to a number of news organisations, saying the nation would not spy on one of its allies. It implied that there may have been an ulterior motive behind the claims.
"These allegations are utterly false," a senior official in the Israeli Prime Minister's office said. "The state of Israel does not conduct espionage against the United States or Israel's other allies."
“The false allegations are clearly intended to undermine the strong ties between the United States and Israel and the security and intelligence relationship we share,” they continued.