The United States turned down Israeli requests for military hardware to help it prepare for a possible attack on Iranian nuclear facilities, according to an Israeli newspaper.
An unsourced report on Wednesday in Haaretz said the US had warned Israel against carrying out any such attack and had refused to supply offensive military hardware. Instead it offered to improve Israel's defences against surface-to-surface missiles.
Defence Minister Ehud Barak did not deny the report, but refused to discuss it: "It would not be right to talk about these things," Mr Barak said.
The West accuses Iran of trying to develop nuclear weapons. Iran denies this and says its nuclear programme is simply to generate electricity. It has vowed to retaliate against Israel and the US if attacked.
Israel, which has the Middle East's only nuclear arsenal, says a nuclear-armed Iran could threaten its existence.
The newspaper report did not specify what weapons systems Israel had requested. It said the US had told Israel its aircraft would be denied permission to use Iraqi airspace to reach Iran.
Mr Barak said Iran was a "threat to the whole world order, and there are many actions to be made in the realm of intelligence and preventive measures".