Iranians hold up pictures of Hezbollah leader Hassan Nasrallah, who was killed in an Israeli airstrike on Beirut’s southern suburbs on September 27, during an anti-Israel protest in Tehran’s Palestine Square on September 30.

Hossein Beris/Middle East Images/AFP via Getty Images

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Hossein Beris/Middle East Images/AFP via Getty Images

Iran is ready to launch airstrikes against Israel, two senior US officials said, after Israel killed Hezbollah leader Hassan Nasrallah in Lebanon last week.

A senior White House official, who spoke on condition of anonymity to discuss security issues, said there were signs that Iran was preparing for the imminent launch of a ballistic missile attack.

“We are actively supporting defense preparations to defend Israel against this attack. “A direct military attack by Iran against Israel will have serious consequences for Iran,” the official said.

In Israel, the U.S. Embassy issued a warning asking all “U.S. government employees and their family members to shelter in place until further notice.”

The threat builds on existing tensions across the region as Israel battles Hezbollah militants in Lebanon and continues its war against Hamas in Gaza – both groups backed by Iran.

Israel began a ground operation in southern Lebanon on Monday.

An anonymous Israeli security official told NPR that Israeli troops had entered Lebanon and attacked Hezbollah military bases near the border. The official said the military was “operating in a limited area and focusing on the villages directly on the border.” Some houses are 100 meters from the border, some tens of meters from the border and some hundreds of meters from the border.”

The Israeli ground offensive comes as Israel ramps up its overall operations against Hezbollah.

Israeli airstrikes across Lebanon have killed more than 1,000 people and forced many civilians to flee their homes in the past two weeks, according to the Lebanese Health Ministry. The attacks targeted Hezbollah and its weapons, killing Nasrallah and several other top officials, as well as many civilians.

Hezbollah began firing rockets into northern Israel on October 8, a day after Hamas launched a major attack on southern Israel. Hezbollah describes its operation as an act of solidarity with the Palestinians.

Over the past year, Israel and Hezbollah have fired almost every day across the Israel-Lebanon border. But shootings remained relatively low until Israel launched a much larger campaign two weeks ago.

Iran has not yet responded militarily to recent Israeli actions against Hezbollah, a group that Iran has founded, trained and armed over the past four decades.

Back in April, an Israeli strike killed several Iranian Revolutionary Guard leaders in Damascus, Syria.

Iran responded by attacking Israel with more than 300 drones and missiles, but almost all were intercepted by Israel and its allies, including the United States. Some rockets caused some damage. Israeli officials said a 7-year-old girl was seriously injured and a military base in southern Israel suffered minor damage.