Shapiro served as Deputy Assistant Secretary of Defense for the Middle East until January—charged with, among other things, considering scenarios in which tensions between Israel and Iran escalated into all-out war and preparing U.

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.

Iran's top diplomat Abbas Araghchi said Saturday that Israel's strikes on his country were undermining nuclear talks with the United States. Araghchi, in a call with Russia's Foreign Minister Sergei Lavrov,

Iraq on Saturday called on the United States to prevent Israeli aircraft from breaching Iraqi airspace to carry out attacks against Iran, citing bilateral agreements and international law.

Israeli Prime Minister Benjamin Netanyahu on Saturday vowed intensified strikes on Iran, declaring that "what they have felt so far is nothing compared with what they will be handed in the coming days",

Tehran said American bases in the Middle East could face reprisals if the U.S. helped repel Iranian attacks on Israel.

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

National security experts warn that Israel's attack on Iran shows why Chinese land and asset purchases in the U.S. pose a significant threat to American security.