At least nine Americans have been killed in Israel since Saturday as a result of attacks launched by the Hamas militant group, according to an official with the United States National Security Council.

"At this time, we can confirm the death of nine U.S. citizens," the official told ABC News in a statement on Monday. "We extend our deepest condolences to the victims and to the families of all those affected, and wish those injured a speedy recovery. We continue to monitor the situation closely and remain in touch with our Israeli partners, particularly the local authorities."

Two French citizens are among those killed in Israel, the French Foreign Ministry said.

-ABC News' Molly Nagle

The United States is warning against other countries from becoming involved in the Israel-Gaza conflict amid fears that it could spread into a wider war in the Middle East.

"This is not the moment for other parties who are hostile to Israel to seek advantage or to seek to exploit the attacks that have taken place," Jon Finer, deputy national security adviser to U.S. President Joe Biden, Monday on "Good Morning America."

"That is part of why the United States has moved the Carrier Strike Group to the eastern Mediterranean to send a strong and unmistakeable signal that no one else should get involved in this," he added. "We'll see how things unfold in the course of the coming days."

Finer also emphasized that the U.S. believes "Israel has every right to defend itself full-stop."

"Israel will ultimately make the decisions about how it chooses to go about and conduct that defense," he said. "We are offering support in a number of ways."

Finer noted that "more U.S. steps to show support and solidarity for Israel" can be expected.

"The U.S. is going to offer support at every level for Israel's defense and we are working through details those details with our intelligence professionals, our military and our diplomats," he added. "We are in daily -- in fact, many times a day -- contact with Israeli counterparts to see what they need and offer it."

The U.S. "strongly suspect[s] that there will be American citizens among those killed" in the ongoing conflict, according to Finer.

"We are looking obviously very intensively into whether there were any Americans were among those who have been abducted and brought to Gaza. This is still ongoing," he said. "There is still fighting inside Israel as we speak and there is a bit of fog of war in terms of the ability to gather specific information. And so, we will have much more to say about this at the right time."

When asked for comment on a recent report by The Wall Street Journal that Iran was behind Hamas' latest attack on Israel, Finer responded: "We have no direct information to confirm that report. We've obviously seen it, we're looking into it, but we do not have the ability to corroborate it at this time."

"What we can be quite clear about is that Iran is broadly complicit in these attacks for having supported Hamas going back decades -- for having provided financial support, for having provided training, for having provided weapons to Hamas," he added. "What we don't have is direct information that shows Iranian involvement in ordering or planning the attacks that took place over the last couple days. It's something that we’re going to keep looking at closely."

At least 33 Palestinian children have been killed in the Gaza Strip since Saturday morning as Israel continues its retaliatory airstrikes, according to the advocacy group Defense for Children Palestine.

-ABC News' Joe Simonetti

Four Israeli hostages were killed alongside their militant captors in the Gaza Strip by Israeli airstrikes on Sunday night and Monday morning, according to Abu Ubaida, spokesman for the Izz ad-Din al-Qassam Brigades, the military wing of Hamas.

There was no official confirmation on the hostage deaths from the Israeli side.

-ABC News' Joe Simonetti.

A State Department official said Monday night that the department has offered 4,000 American citizens and their immediate family members help to depart Israel via government-organized transportation since Friday.

“Since Oct. 13, we have augmented the limited commercial flight availability by offering more than 4,000 seats on U.S. government-chartered transport by air and sea to U.S. citizens and their immediate family members,” one official said. “We have communicated the availability of departure assistance options for U.S. citizens via targeted, individualized messaging as well as via broad public messaging.”

Departing flights, though, were not nearly at capacity, the official said.

“The departure options we have offered have generally departed at half capacity or less. Nearly 1,000 U.S. citizens and their immediate family members have departed on U.S. government-chartered transport,” an official said.

The official added that 3,000 other American citizens have told the State Department that they were able to leave Israel and the West Bank on their own.

-ABC News’ Shannon Crawford