"We've spoken in the past to our concern ... about leaks of certain sensitive information. And obviously, we've taken steps to ensure that the negotiations remain private," State Department spokeswoman Jen Psaki said.
But she refused to either confirm or deny a Wall Street Journal report citing anonymous US officials accusing Israel of spying on the nuclear negotiations with Iran aimed at reaching a deal that Israeli Prime Minister Benjamin Netanyahu vociferously opposes.
"We still have ongoing conversations that are continuing with Israel," Psaki said, adding the Obama administration would continue to brief Israeli officials in private.
Current and former US officials quoted in the Journal said they believed Israel had passed on the information to US lawmakers aiming to undermine support for the emerging deal, which has been championed by the White House.
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But Psaki said it was an "absurd notion that Congress would have to rely on any foreign government to gain insight into the nuclear negotiations with Iran."
Since October 2013, just before an interim deal was agreed with Iran, US officials had conducted some 230 briefings and calls with Senate and House lawmakers and their staff on the substance of the discussions.
"We have briefed Congress on the nuclear talks as much or perhaps more than any other issue," Psaki insisted.
"Congress has been briefed extensively, thoroughly and frequently. So my point is that it's absurd that they would need information from a foreign country."
Israel has flatly denied the spying accusations, with Foreign Minister Avigdor Lieberman denouncing the report as "incorrect and inaccurate" and Intelligence Minister Yuval Steinitz saying it was full of "lying allegations."