Israel has spied on US negotiations over Iran's nuclear programme and fed the obtained intelligence to Republican Congress members in order to undermine support for the talks, the Wall Street Journal reported.

The Israeli effort was part of a campaign to help build a case against the emerging terms of a deal, the Wall Street Journal reported on Monday, citing current and former US officials without naming them.

"It is one thing for the US and Israel to spy on each other. It is another thing for Israel to steal US secrets and play them back to US legislators to undermine US diplomacy," the newspaper quoted a senior official as saying.

The report said that the US discovered the information breach when US intelligence intercepted Israeli cables in which details of the negotiations were discussed.

Confronted with the discovery, Israeli officials denied their country was spying on the nuclear talks, saying they received the information through other sources, the report said.