Israel's Prime Minister Benjamin Netanyahu said on Sunday that he was unaware of any talks between the United States and Iran over the Islamic republic's nuclear programme.
"Israel doesn't know about these contacts and I can't confirm that they've actually taken place," Netanyahu said in a statement.
"I can say that Iran used the talks and negotiations with the Five Powers to drag its feet and to gain time to advance its nuclear weapons programme," he added.
Deputy premier and senior cabinet minister Moshe Yaalon had told Israeli public radio on Sunday he was aware of US attempts to directly negotiate with Iran over its nuclear programme, but did not believe the talks had actually taken place.
"It's no secret that there were attempts to use the fact the United States participated in the P5+1 talks and met Iranians in these meetings to also create direct contact with Iran," Yaalon said.
Negotiations between the so-called P5+1 global powers -- Britain, China, France, Germany, Russia and the United States -- and Tehran over its nuclear programme have stalled, with tough sanctions aimed at forcing a breakthrough.
Yaalon's remarks came after the New York Times reported that Washington and Tehran had agreed to one-on-one negotiations over Iranian atomic ambitions in a report swiftly denied by the White House.
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Speaking to Israel public radio, Yaalon said that Iran was, "in principle, against this, up to this moment."
"I believe the White House denial at this point."
Netanyahu said: "In the last year alone, in the course of these talks, Iran has enriched thousands of kilograms of uranium in its nuclear programme.
"And I don't see any reason why they wouldn't continue in that same way if they open up talks with the US... as long as I am the prime minister, Israel will not allow Iran to reach a military nuclear capability."
Israel and Western powers accuse Tehran of seeking to develop a nuclear bomb, charges which Iranian leaders deny, saying their nuclear energy programme is purely for civilian purposes.
Israel, the Middle East's sole, if undeclared, nuclear power, has refused to rule out a military strike to prevent Iran from attaining nuclear military capabilities.
According to Yaalon, who serves as strategic affairs minister, Israel would be the main beneficiary of a peaceful resolution.
"If Iran ended its military nuclear programme as a result of direct talks between it and the US -- we would be the first to welcome it," he said.