The White House stated on Thursday that Iran can produce a nuclear weapon in a matter of two weeks once its supreme leader, Ali Khamenei, gives the green light.
"Let's be very clear, Iran has all that it needs to achieve a nuclear weapon," White House press secretary Karoline Leavitt said at her briefing. "All they need is a decision from the supreme leader to do that."
"And it would take a couple of weeks to complete the production of that weapon, which would, of course, pose an existential threat not just to Israel but to the United States and to the entire world," she added.
Israel and Iran's air war entered a second week on Friday and European officials sought to draw Tehran back to the negotiating table after President Donald Trump said any decision on potential US involvement would be made within two weeks.
Israel began attacking Iran last Friday, saying it aimed to prevent its longtime enemy from developing nuclear weapons. Iran retaliated with missile and drone strikes on Israel. It says its nuclear program is peaceful.
Israeli air attacks have killed 639 people in Iran, the Human Rights Activists News Agency said. Those killed include the military's top echelon and nuclear scientists. Israel has said at least two dozen Israeli civilians have died in Iranian missile attacks.
Israel has targeted nuclear sites and missile capabilities, and sought to shatter the government of Supreme Leader Ali Khamenei, according to Western and regional officials.
Iran has said it is targeting military and defence-related sites in Israel, although it has also hit a hospital and other civilian sites.
Israel accused Iran on Thursday of deliberately targeting civilians through the use of cluster munitions, which disperse small bombs over a wide area. Iran's mission to the United Nations did not immediately respond to a request for comment.