The US State Department has released a series of documents from 1969-1972 related to US policy toward Israel, including intense efforts by the Nixon Administration to try to prevent Israel from acquiring nuclear arms, and to convince them to join the nuclear non-proliferation treaty (NPT).
The US had gotten a concession from then deputy DM Shimon Peres in the early 1960’s that Israel would not be the first nation to introduce nuclear weapons to the region, which the US interpreted at the time as them not getting nuclear arms.
Israeli officials, rather, saw this as meaning they could make all the nukes they wanted so long as they kept them a secret. The Nixon Administration then sought to get a written assurance they wouldn’t produce nuclear warheads, and pushed for them to sign the NPT by year’s end, saying Israel spent years “delaying” on that issue.
Ultimately, Israel was only willing to reiterate the promise not to introduce nuclear weapons to the region, and the US let the matter slide. Nearly 50 years later, Israel has a major nuclear arsenal, but is still operating under the theory that if they don’t formally talk about it, they’re complying with pledges to the US.