The debate over the sanctions has already provoked rare interventions from British Prime Minister David Cameron and the head of Israel's intelligence service, who met with U.S. lawmakers over the weekend.
Exactly what Mossad chief Tamir Pardo said to the visiting U.S. senators was a subject of yet more argument on Thursday.
Secretary of State John F. Kerry told reporters on Wednesday that the Israeli intelligence chief had made an impassioned case against new sanctions, saying that they would be akin to "throwing a grenade into the process.” Such a position would have put him at odds with the Israeli prime minister.
Pardo, meanwhile, denied saying any such thing during a Jan. 19 meeting with the Americans. Instead, the Mossad director said he reiterated that "firm pressure" was needed "to bring about meaningful compromises from the Iranian side."
"Despite what was reported, the head of the Mossad did not say he opposes additional sanctions against Iran," said a Mossad statement issued through the prime minister's office. "The head of the Mossad emphasized in the meeting the extraordinary effectiveness of the sanctions against Iran, for a number of years, in bringing Iran to the negotiating table.”