In a private email exchange last year leaked this week by hackers, former Secretary of State Colin Powell discussed Israel's nuclear weapons capability with a friend, saying the country has 200 warheads.

Though Israel is widely believed to have developed nukes decades ago, it has never declared itself to be a nuclear state. The existence of its weapons program is considered classified information by both the Israeli and U.S. governments.

Powell, a retired Army general who has served as White House national security adviser and chairman of the Joint Chiefs of Staff, told The Associated Press on Friday through a spokeswoman he was referring to public estimates of Israel's nukes.

"Gen. Powell has not been briefed or had any knowledge from U.S. sources on the existence and or size of an Israeli nuclear capability," the statement said. "He like many people believe that there may be a capability and the number 200 has been speculated upon in open sources." It added: "This email was written 10 years after he left government and has not received briefings on classified matters."

Powell, 79, would not say whether he still retains a security clearance.

In the March 2015 exchange from his personal Gmail account, Powell was discussing a speech that day to a joint session of Congress by Israeli Prime Minister Benjamin Netanyahu. The conservative Israeli leader staunchly opposed the deal then proposed by President Barack Obama to curb Iran's nuclear weapons program.

"Iranians can't use one if they finally make one," Powell wrote to Democratic donor Jeffrey Leeds, a hedge-fund founder who serves on the board of the Colin L. Powell School for Civic and Global Leadership at the City College of New York. "The boys in Tehran know Israel has 200, all targeted on Tehran, and we have thousands."

Itai Bardov, spokesman for the Israeli Embassy in Washington, declined to discuss Powell's email or his nation's policy of not commenting on whether it has nuclear weapons.

Asked about the issue at a briefing Friday, State Department spokesman John Kirby also declined to comment.

"I'm not going to discuss matters of intelligence," Kirby said. "We support the nuclear nonproliferation treaty."

Powell is not the first top-level U.S. government official to publicly discuss Israel's nukes. Former President Jimmy Carter has said in interviews and speeches that Israel has between 150 and 300 warheads.

But the issue is not supposed to be discussed openly by those who work for the U.S. government and hold active security clearances. Even members of Congress are routinely admonished not to even mention the existence of an Israeli nuclear arsenal, said Avner Cohen, a professor at the James Center for Nonproliferation Studies at the Middlebury Institute of International Studies at Monterey.

"It's noteworthy that someone like Colin Powell said that," said Cohen, who has written extensively about Israel's nuclear program. "Obviously, he was privy to all kinds of intelligence on this issue. It's kind of considered by everybody to be a public fact, but the United States government as a matter of policy has never said that."

Cohen said U.S. intelligence on Israel's nuclear program carries "top level" classification. As an indication of the subject's sensitivity, he pointed to the recent case James Doyle, a political scientist at Los Alamos National Laboratory in New Mexico who lost his job after publishing an academic paper in 2013 that included Israel on a list of nations that either "possess nuclear arms or are in alliance with nuclear powers."

Powell's leaked email, which was among thousands of his messages posted earlier this week to the website DCLeaks.com, provides fodder for defenders of Hillary Clinton's use of a private email server while she served as secretary of state from 2009 to 2013. The Democratic presidential nominee has faced withering criticism from Republicans for exchanging emails with her aides that contained sensitive government information.

Powell also used a private America Online email account to communicate with senior U.S. officials and foreign dignitaries while serving as the nation's top diplomat under President George W. Bush. A Republican, Powell said he never discussed classified information over his private account.

DCLeaks.com has been alleged to be an outlet for hackers tied to Russian intelligence. The website, which says it intends to expose the misuse of political power, has released emails from other Washington political figures.

The release of Powell's emails is the latest in a string of leaks that appear intended to influence the 2016 presidential election. The FBI is investigating how thousands of Democratic National Committee emails were hacked and published, an embarrassing breach that Clinton's campaign maintains was committed by Russia to benefit Donald Trump.

In his emails leaked this week, Powell called the GOP presidential nominee "a national disgrace" and suggested his own Republican Party is "crashing and burning." He also lamented Clinton's attempt to equate her use of private email at the State Department with his.