An Israeli air strike killed two people in Damascus Wednesday, a monitor said, in the second strike in two days on a neighborhood that is home to security headquarters and embassies.

"An Israeli air strike targeted a residential building in the Mazzeh neighborhood frequented by Hezbollah leaders and the Iranian Revolutionary Guards," killing at least two people whose identity was not immediately clear, the Britain-based Syrian Observatory for Human Rights said.

The U.S. has imposed sanctions on an Iranian man and three Chinese firms that Washington believes helped the Houthi militant group acquire materials needed to manufacture and deploy advanced missiles and drones against the U.S. and its allies.

Iranian citizen Hasan Ahmad Hasan Muhammad al-Kuhlani is named in the sanctions announced Wednesday. He is accused of facilitating weapons smuggling for the Houthis.

World leaders called on Iran and Israel to step back from the brink after Tehran fired a barrage of rockets at its arch-rival.

Tehran said Tuesday's attack -- launched as Israel said it was mounting a ground offensive against Iran-backed Hezbollah in Lebanon -- was in response to the killings of Iran-backed militant leaders.

Israel on Wednesday declared U.N. chief Antonio Guterres "persona non grata", banning him from entering the country for failing to condemn Iran's missile attack on Israel.

"Anyone who cannot unequivocally condemn Iran's heinous attack on Israel does not deserve to step foot on Israeli soil. This is an anti-Israel Secretary-General who lends support to terrorists, rapists, and murderers," said Foreign Minister Israel Katz in a statement.

The Health Ministry in Gaza said at least 51 people were killed and 82 wounded in the operation in Khan Younis that began early Wednesday. Records at the European Hospital show that seven women and 12 children, as young as 22 months old, were among those killed.

Another 23 people, including two children, were killed in separate strikes across Gaza, according to local hospitals.

The Biden administration says there is a significant difference between Israeli actions that have expanded its war against the Iranian-backed militant groups Hamas and Hezbollah and Iran's retaliatory missile attack against Israel, which it condemned as escalatory.

In carefully calibrated remarks, officials across the administration are defending the surge in attacks by Israel against Hezbollah leaders in Lebanon, while still pressing for peace and vowing retribution after Iran fired about 200 ballistic missiles at Israel on Tuesday.

Israeli police said on Wednesday that a total of seven people were killed in a shooting attack in Tel Aviv on Tuesday evening minutes before the Iranian missile barrage.

Two Palestinian men from the Israeli-occupied West Bank city of Hebron opened fire in the Jaffa neighborhood of Tel Aviv, including shooting directly into a light rail carriage crowded with passengers that was stopped at a station.

Air traffic was halted at Israel's Ben Gurion airport on Tuesday, a spokesman said, as blasts rocked the country after Iran launched a missile attack.

Iran's Revolutionary Guards said the missile attack under way against Israel was in response to the killing of Hezbollah chief Sayyed Hassan Nasrallah last week as well as that of the Hamas leader.

"The United States has indications that Iran is preparing to imminently launch a ballistic missile attack against Israel," a senior White House official told AFP on Tuesday, speaking on condition of anonymity.

"We are actively supporting defensive preparations to defend Israel against this attack," the official said in a statement, warning that such an action "will carry severe consequences for Iran."

A Syria war monitor said six people including three civilians were killed in Israeli strikes early Tuesday targeting Damascus and its vicinity, amid fears of broader Israeli raids on the country.

The Syrian Observatory for Human Rights said the strikes targeted two vehicles in Damascus's upscale Mazzeh district, as well as "air defense batteries at the (city's) airport, and the vicinity of the Kisweh area", south of the capital.