Israel-Gaza updates: Israeli forces preparing for 'wide range of offensive plans'

An emergency meeting of the United Nations Security Council failed to condemn the Hamas attacks on Israel Sunday evening.

Deputy U.S. Ambassador the U.N. Robert Wood said the situation was "still fluid" and "very dangerous."

"What is important now is that the international community needs to show its solidarity with Israel. We have Israel's back fully as the United States, and the condemnation of Hamas needs to continue until they end this violent terrorist activity against the Israeli people," Wood said after the meeting.

-ABC News' Ellie Kaufman

At least four American citizens were killed in the attacks in Israel over the weekend, senior administration officials told top House lawmakers on a call Sunday evening, according to multiple sources familiar with the matter.

That figure could rise in the coming days, the Biden administration officials told Congress. The administration is also still investigating unconfirmed reports of American citizens being taken hostage by Hamas.

Participants on the call included senior members of the relevant House committees and party leaders — including Rep. Patrick McHenry, R-North Carolina, the temporary House speaker, two sources told ABC News.

As previously reported, Senate leaders will receive a similar briefing tonight.

--ABC News' Ben Siegel

Senate leadership, chairs and ranking members of relevant committees will receive an unclassified briefing on the situation in Israel Sunday night at 9 p.m. ET, a Senate source told ABC News.

The chairs and ranking members from the Senate Committee on Foreign Relations, the Senate Select Committee on Intelligence and the Senate Committee on Armed Services are among those who will be briefed.

The president of Iran -- Ebrahim Raisi -- called the attack by Hamas on Israel as a “victory,” Reuters reported on Sunday.

At a cabinet meeting, he referred to the attack as a “manifestation of resistance,” the outlet also reported.