Israel has 200 nuclear weapons, former US secretary of state Colin Powell said in a leaked email, part of a trove that has been released online.
Powell himself has confirmed the emails are real. The message in question pertains to the Iranian nuclear negotiations, which President Barack Obama concluded last year.
"Anyway, Iranians can't use one if they finally make one. The boys in Tehran know Israel has 200, all targeted on Tehran, and we have thousands," Powell said.
LobeLog, a foreign policy blog in the US, first reported on the emails pertaining to Iran and Israel.
Israel is not a signatory to the Nuclear Non-Proliferation Treaty and has tried to maintain some sense of ambiguity as to whether it actually has nuclear weapons.
However, leaks since the 1980s, including by whistleblower Mordecai Vanunu, have shown Israel's nuclear programme in the southern city of Dimona has offensive capabilities.
The programme in Dimona was founded by Shimon Peres, the 93-year-old former president currently in hospital after suffering a stroke.
The US - Israel's main backer - has played along for the most part with Israel's ambiguity. This week, Washington and the Israelis inked a 38-billion-dollar deal in military assistance to Israel over the next 10 years.
In the emails, Powell appeared to reject an Israeli talking point that at the time of the deal Tehran was just a year away from making a bomb.
"Bibi likes to say 'a year away,' as do our intel guys. They say it every years. I ain’t that easy to do [sic]," Powell wrote, referring to Israeli Prime Minister Benjamin Netanyahu.
He ultimately called the nuclear deal "pretty good" and supported the Obama administration's negotiated agreement. Powell was secretary of state under president George W Bush from 2001 to 2005.