At least 600 people in Israel have been killed in the surprise attacks by Hamas and at least 370 have been killed in retaliatory strikes in Gaza, Israeli and Palestinian health officials said Sunday.

At least 2,156 people have been injured in Israel, according to the Israeli Health Ministry. At least, 2,200 have been injured in Gaza, the Palestinian Health Authority said.

-ABC News' Joseph Simonetti

Republican presidential candidate Chris Christie slammed the dysfunctionin> the U.S. House of Representatives, where a small group of Republican lawmakers last week voted along with the Democratic minority to oust Speaker Kevin McCarthy, for leaving it without a way to pass legislation, including foreign aid to Israel.

"What I would be doing is making sure, one, that Israel has everything that it needs to be able to take whatever actions it needs to take. And this is the problem with not having a speaker right now," Christie, the former New Jersey governor, told ABC News' "This Week" anchor George Stephanopoulos.

Christie, a former ABC News contributor, added, "The actions taken by some members of my party were wholly irresponsible without this going on. They're now even putting a brighter light on the irresponsibility of not having someone in place."

Christie also said his top priorities if he were president would be engaging allies in the region, such as Jordan and Saudi Arabia, to keep the conflict from spreading and to serve as a "sounding board" to Israeli Prime Minister Benjamin Netanyahu to help him "think through the ramifications of every step they're going to take to defend themselves and to try to do the best they can to eliminate the leadership of Hamas."

-ABC Nicholas Kerr

For the first time since Saturday's surprise attack by Hamas militants, the Israeli government confirmed that a number of people, including civilians, have been taken hostage.

Israel's Government Press Office said Sunday that at least 100 Israeli citizens and soldiers are being held hostage by Hamas fighters.

U.S. Secretary of State Antony Blinken said in separate interviews on CNN and NBC News that there is a possibility Americans are among those killed or taken hostage and that the U.S. Department of State is investigating.

-ABC News' Joe Simonetti

Secretary of State Antony Blinken on Sunday pushed back on growing Republican criticism that the White House's decision to allow the transfer of some $6 billion of Iran's oil revenue, in exchange for the release of five American detainees, was a sign of "appeasement" ahead of the surprise attack on Israel by Hamas militants.

"Not a single dollar from that account has been spent to date and, in any event, is very closely and carefully regulated by the Treasury Department," Blinken told ABC's "This Week" anchor George Stephanopoulos.

Blinken stressed that the funds are designated solely for humanitarian purposes and are not U.S. tax dollars.

-ABC News' Adam Carlson

As the Biden administration intensifies efforts to help American nationals leave Israel and Gaza, more than 20,000 U.S. citizens have reached out to the State Department asking for help in the wake of the Hamas attacks, including several hundred seeking to leave Gaza, according to two U.S. officials.

While not all have actively sought assistance with transportation, "many thousands" across Israel have indicated they needed help finding flights out of the country, the officials said.

Government-chartered planes have now started to ferry U.S. citizens from Israel to other countries in the region, though one official said the State Department still cannot share a detailed breakdown on the number of Americans whose departure it has already facilitated or the number of Americans still waiting for help "given this is an unfolding situation."

For Americans in Gaza, the U.S. is still eyeing the Rafah border crossing between Gaza and Egypt as a means of safe passage. Officials say they are very hopeful they will be able to work with Israel and Egypt to establish a corridor for U.S. citizens and other foreign nationals, but that it could take days to make substantial progress.

The Israeli government estimated that between 100 to 130 Americans were living in Gaza earlier this year. An official says the State Department believes hundreds more are visiting -- putting the total number in Gaza potentially between 500 and 600.

The State Department estimates that roughly 500,000 American citizens reside in Israel.

-ABC News' Shannon K. Crawford