Israel says such evidence is concrete proof that Iran is well on its way to reaching weapons capability, perhaps in the coming months.
Differences with the U.S. over how to deal with Iran have boiled over into palpable tensions in recent weeks.
Earlier this week, U.S. State Department spokeswoman Victoria Nuland said "it is not useful" to be setting deadlines or outlining "red lines." She also noted that Obama has stated unequivocally that the United States will not allow Iran to obtain a nuclear weapon.
On Tuesday, she said the Iranian situation is a matter of "intense discussion" with Israel. She declined to elaborate, saying she did not want to conduct diplomacy in public.
But privately, U.S. officials have bristled at how Israel has publicly played up the differences and publicly lectured Washington on its responsibilities.
They have also been irked by what they see is Netanyahu's attempts to exploit the campaign season to push the U.S. into difficult positions. The officials spoke on condition of anonymity because they were discussing a sensitive diplomatic matter.
Though they stopped short of accusing Netanyahu of taking sides in the election, the Israeli prime minister has a longtime relationship with Republican candidate Mitt Romney and with Sheldon Adelson, a casino magnate and top donor to the Republican Party. Romney, who visited Israel in July, has repeatedly criticized Obama's handling of the nuclear issue.
Obama and Netanyahu have long had a rocky relationship, because of policy differences and a lack of personal chemistry. In one famous incident, a frustrated Obama left a White House meeting with Netanyahu to go eat dinner with his family.
U.S. and Israeli officials confirmed Tuesday that Obama would not meet with Netanyahu when the Israeli leader goes to New York for the U.N. General Assembly later this month. Both sides cited scheduling issues and rejected suggestions that Netanyahu had been snubbed.
In a veiled criticism of Netanyahu, his own defense minister, Ehud Barak said preserving good relations with the U.S. was essential and that all disagreements should be handled quietly.
"These differences should be smoothed over, between us, behind closed doors. We should not forget that the U.S. is the main ally of Israel," Barak said.
The U.S. has led efforts in the U.N. Security Council to impose several rounds of economic sanctions on Tehran. In July, the European Union banned oil imports from Iran, just after the U.S. enacted tough measures against Iran's central bank.
While there are signs that the sanctions are harming Iran's economy, Israeli officials believe it has not altered their pursuit of a nuclear bomb.
Israelis are astounded that Iran continues to be one of the leading oil producers, because exports have continued almost unabated to China, India and other points in Asia. Israel yearns for even tighter oil sanctions and a total boycott of Iran's central bank, crippling its ability to conduct trade.
The Israeli efforts may be bearing some fruit: Last week several European Union foreign ministers said they would support tougher sanctions on Iran. And Canada on Friday severed diplomatic relations with Iran, accusing the Islamic Republic of being the most significant threat to world peace. An Iranian semi-official news agency says Iran expects more countries to follow Canada's example and close their embassies in Tehran.
Looming in the background is Israel's threat to use force against Iran, a risky operation that could set off mayhem across the region. U.S. officials have made clear they oppose a unilateral Israeli attack. The U.S. military chief, Gen. Martin Dempsey, recently said he would "not want to be complicit" in such an assault.
The window for Israeli military action is more limited than for the Americans, who possess more powerful "bunker-busting" bombs.
For that reason, the Israelis believe a clear "red line" set by the U.S. would not only send a powerful message to Iran, it would also reduce the need for military action.