U.S. President Barack Obama will not pressure Israel to disclose its nuclear arsenal to international inspection, as reported on Friday by The Washington Times, Haaretz reported.
The 40-year-old covert agreement between the U.S. and Israel has allegedly permitted Israel to maintain an active nuclear facility without inspection that contains several hundred nuclear bombs.
The joint understanding was apparently reached during Prime Minister Benjamin Netanyahu's visit to the White House in May this year.
The report also said that the senior officials who had confirmed these findings spoke on the condition that they would not be named.
Israel was nervous Obama would retract U.S. understanding of the secret treaty signed in September 1969 in a summit between former U.S. President Richard Nixon and the then Israeli Prime Minister Golda Meir, the report added.
To date there is no official documentation of such an agreement nor has it ever been acknowledged by any U.S. or Israeli government.
The report follows a United Nations nuclear assembly resolution which urged Israel earlier this month to put all its atomic sites under the world body's inspection and join the Non-Proliferation Treaty.
Israel deplored the measure for singling it out while many of its neighbors remained hostile to its existence, and said it would not cooperate with it.
The non-binding resolution, which passed for the first time in 18 years of attempts thanks to more developing nation votes, voiced concern about "Israeli nuclear capabilities" and urged the International Atomic Energy Agency to tackle the issue.
Israel is one of only three countries worldwide along with India and Pakistan outside the nuclear NPT and is widely assumed to have the Middle East's only nuclear arsenal, though it has never confirmed or denied this.
UN Security Council members Russia and China also backed the resolution, which passed by 49 votes to 45 against in a floor vote at the IAEA's annual member states conference.
The vote split along Western and developing nation lines. There were 16 abstentions.
"Israel will not cooperate in any matter with this resolution which is only aiming at reinforcing political hostilities and lines of division in the Middle East region," chief Israeli delegate David Danieli told the chamber.
Western states said it was unfair and counterproductive to isolate one member state. They said an IAEA resolution passed on Thursday, urging all Middle East nations to foreswear atomic bombs, included Israel and made Friday's proposal unnecessary.
Arab nations said Israel had brought the resolution on itself by having never signed the 40-year-old NPT.
Before the vote, U.S. Ambassador Glyn Davies said the resolution was "redundant ... Such an approach is highly politicized and does not address the complexities at play regarding crucial nuclear-related issues in the Middle East."
Calling the resolution "unbalanced", Canada tried to block a vote on the floor with a "no-action motion". But the procedural maneuver lost by an eight-vote margin. The same motion prevailed in 2007 and 2008.
A senior diplomat from the non-aligned movement of developing nations said times had changed.
"People and countries are bolder now, willing to call a spade a spade. You cannot hide or ignore the truth, the double standards, of Israel's nuclear capability forever," he said.