The United States is the main international backer of Israel, Iran's biggest regional foe. It is also a close ally of Sunni Gulf monarchies which for years pursued their own rivalry with the Islamic Republic, seeing it as their main regional threat.

After decades of enmity and conflict by proxy, it is the first time the arch-enemies have traded fire with such intensity, triggering fears of a prolonged conflict that could engulf the Middle East.

The two sides were scheduled to meet for a sixth round of negotiations on Sunday. Oman, which was set to host the talks, said on Saturday that this round had been canceled.

The United States has pulled some diplomatic staff and military families out of the Middle East, citing unspecified regional security risks.

Countries trade strikes as tensions grow over larger Middle East conflict - Iranian missiles struck an apartment building in the Galilee region, killing four people, as the countries exchanged fire

In sweeping attacks that started early Friday, Israel has struck at the regime in Tehran, targeting Iranian nuclear and military assets. The Israeli strikes have killed more than 70 people, including four top security chiefs, and damaged Iran’s main nuclear site at Natanz.

Iran launched multiple deadly waves of missiles and drones toward Israel into Saturday morning following Israel’s unprecedented strikes aimed at destroying Iran’s nuclear program and decapitating its military leadership.

Iranian officials said on Friday that the United States "shall be held fully accountable" for its support of Israel after the nation took out key Iranian nuclear facilities and killed government leaders in a series of air strikes this week.