National security adviser Jake Sullivan urges Israel to lower intensity of military campaign in Gaza

National security adviser Jake Sullivan touched down in Israel on Thursday with a blunt message from the Biden administration imploring the Israeli government to lower the intensity of its sweeping military campaign in Gaza as soon as possible, U.S. officials told ABC News.

The officials said that the administration will stand behind Israel as it seeks to destroy Hamas but that it expects the country's strategy to pivot from an all-out assault and toward more targeted, tactical operations aimed at eliminating Hamas' leaders and hideouts, as well as recovering hostages.

White House spokesperson John Kirby declined to set any specific timeline for the transition during a Thursday press briefing but said that Sullivan discussed it happening "during the near future" during his face-to-face meetings with Prime Minister Benjamin Netanyahu and the other members of Israel's war cabinet.

Kirby said that Sullivan also reiterated U.S. support for Israel and the administration's commitment to bringing home the scores of hostages still held by Hamas during his meeting with Netanyahu, but that he also "asked hard questions" about the next phase of Israel's offensive and "discussed efforts Israel is now undertaking to be more surgical and precise in their targeting."

President Joe Biden also said Thursday that he wants Israel to "be more careful" with their attacks in Gaza and be focused on "how to save civilian lives" as casualties continue to climb.

"I want them to be focused on how to save civilian lives, not stop going after a Hamas, but be more careful," he said during an event at the National Institutes of Health on Thursday.

The president was asked whether he wanted Israel to scale back its assault on Gaza by the end of the year as reported by The New York Times and move to a lower intensity phase, but he did not address that question.

Israeli officials have not yet publicly commented on their engagements, but local press reports claimed that Defense Minister Yoav Gallant told Sullivan that Israel still needed months of war to stamp out Hamas.

Differing outlooks on how long the full-blown fighting should last is just one potential threat to the coalition between the U.S. and Israel. Growing international and domestic backlash to the conflict have also tested the Biden administration's resolve.

A senior State Department official said that in previous closed-door meetings with U.S. officials, Israel has given vague forecasts regarding how long its campaign will take but that its initial operations in the northern Gaza were completed faster than both countries originally anticipated.

A principal counselor to the president, Sullivan is one of a handful of top-level Washington officials that have been traveling to the Middle East at a routine clip in the aftermath of Hamas' Oct. 7 terrorist attack as the administration attempts to both demonstrate support for Israel and rein in its retaliation, while also seeking to cool tempers in neighboring countries to prevent the conflict from escalating into a regional war.

Senior officials say that each leg of the administration's shuttle diplomacy strategy has been driven by a clear goal, such as convincing the Israeli government to allow desperately needed aid into Gaza or to implement humanitarian pauses in the warfare.

The administration's push for precision in Israel's military operations comes days after Biden delivered some of his harshest criticism for Israel's battle tactics to date, remarking at a campaign fundraiser that the country was beginning to lose international support due to "the indiscriminate bombing that takes place," according to a White House transcript.

While the U.S. hasn't launched any investigation into whether Israel may have committed war crimes in Gaza, administration officials have publicly expressed their dismay at the large numbers of casualties suffered in the enclave.

More than 18,000 people have been killed in Gaza since Oct. 7, according to the Hamas-run Gaza Health Ministry. More than 1,200 people were killed in Israel during Hamas' attacks, according to the Israeli prime minister's office.

State Department spokesperson Matthew Miller on Wednesday said he believed Biden was speaking about Israel's "large-scale bombing campaign that we've seen where thousands of civilians have been killed."

"We've seen too many civilians killed," he added.

The staggering death toll has riled other countries in the region -- including Saudi Arabia, which was previously on a track toward establishing diplomatic ties with Israel, a development the Biden administration says would be instrumental in ensuring long-term peace for the Middle East.

Ahead of his visit to Israel, Sullivan stopped in the Saudi capital, Riyadh, where he met with Prime Minister and Crown Prince Mohammed bin Salman to discuss a number of issues, "including ongoing efforts to create new conditions for an enduring and sustainable peace between Israelis and Palestinians," according to the White House.

ABC News' Mary Bruce, Molly Nagle and Justin Gomez contributed to this report.