Iran launched its first direct military attack against Israel on Saturday.
Israel said it and its allies have intercepted the 'vast majority' of more than 200 drones and missiles launched by Iran.
Hours later, Iran announced it had also launch much more destructive ballistic missiles and cruise missiles.
Iran's Islamic Revolution Guard Corps (IRGC) said the attack was aimed at "specific targets".
Iran had vowed to retaliate for a strike on its consulate in Syria on 1 April which killed seven IRGC officers, including a top commander. It accused Israel of carrying out that attack, but Israel neither confirmed nor denied it.
Netanyahu called a war cabinet meeting after the start of the Iranian attack, and later spoke to President Biden, who said he had reaffirmed "America's ironclad commitment to the security of Israel".
Meanwhile, the United States, Canada and the United Nations have condemned the Iranian air attack on Israel, with President Joe Biden reaffirming America's "ironclad commitment" to the Jewish nation and vowing to convene a meeting of the G-7 leaders on Sunday to develop a coordinated response to the brazen assault.
Biden said "We helped Israel take down nearly all" of them.
His comments came as American forces joined efforts to down drones and missiles launched by Tehran.
"Earlier today, Iran -- and its proxies operating out of Yemen, Syria and Iraq -- launched an unprecedented air attack against military facilities in Israel. I condemn these attacks in the strongest possible terms," Biden said after his call with Israeli Prime Minister Benjamin Netanyahu on Saturday.
In New York, UN Secretary-General, Antonio Guterres in a statement condemned the serious escalation represented by the large-scale attack launched on Israel by Iran. “I call for an immediate cessation of these hostilities,” he said.
“I am deeply alarmed about the very real danger of a devastating region-wide escalation. I urge all parties to exercise maximum restraint to avoid any action that could lead to major military confrontations on multiple fronts in the Middle East,” he said.
Israel and Iran have been on a collision course throughout Israel's six-month war against Hamas militants in the Gaza Strip. The war erupted after Hamas and Islamic Jihad, two militant groups backed by Iran, carried out a devastating cross-border attack on Oct. 7 that killed 1,200 people in Israel and kidnapped 250 others.
An Israeli offensive in Gaza has caused widespread devastation and killed over 33,000 people, according to local health officials.
