WASHINGTON—A secret memorandum that expanded intelligence sharing with Israel after the Oct. 7 Hamas attack has led to growing concerns in Washington about whether the information is contributing to civilian deaths , according to people familiar with the issue.

Among the worries is that there is little independent oversight to confirm that U.S.-supplied intelligence isn’t used in strikes that unnecessarily kill civilians or damage infrastructure, the people said.

The secret U.S.-Israeli intelligence-sharing agreement has received less public scrutiny than U.S. weapons sales to Israel . But it is prompting increasing questions from Democratic lawmakers and human-rights groups, even as alarm mounts within the Biden administration over how Israel is conducting its military campaign in Gaza following Hamas’s Oct. 7 attacks, which killed about 1,200 Israelis.

The concerns about intelligence sharing in some ways mirror those over the provision of American weapons as the death toll mounts in Gaza, and President Biden has left open the possibility of withholding some arms from its closest ally in the Middle East. That possibility hasn’t been raised with intelligence, but its potential for contributing to civilian casualties is being discussed in the administration and on Capitol Hill.

“What I’m concerned about is making sure our intelligence sharing is consistent with our values and our national-security interests,” Rep. Jason Crow (D., Colo.), a member of the House Intelligence Committee, said in an interview.

Crow, who in December wrote to Director of National Intelligence Avril Haines seeking details of the sharing arrangements, added that he worried that “what we’re sharing right now isn’t advancing our interests.”

Israel’s military operation since the Oct. 7 attack has led to the deaths of about 32,000 residents of Gaza, many of them women and children, according to Palestinian health authorities, whose figures don’t distinguish between militants and noncombatants. Israel’s military says the total death toll is roughly accurate but disputes the composition, saying more than one-third of the dead are militants.

Israel’s military operation in Gaza has also destroyed or severely damaged a large swath of civilian infrastructure, including mosques, hospitals and universities. Israel says the widespread destruction is unavoidable because of Hamas’s decision to embed its military infrastructure intentionally within civilian areas to shield itself from Israeli attacks.

Crow said he met separately with a senior Israeli military figure and U.S. intelligence officials and said there were “some pretty big inconsistencies” in the two sides’ accounts of the civilian toll.

The intelligence sharing with Israel is conducted under a secret memorandum that the White House issued shortly after Hamas’s Oct. 7 attack and amended a few days later, U.S. officials said. At about the same time, the U.S. expanded its intelligence collection on Gaza, having largely relied on Israel to spy on the enclave in recent years.

At the start of the war, the U.S. intelligence community framed guidelines for sharing intelligence with their Israeli counterparts, but top White House policymakers ultimately determine whether any violation has occurred, people familiar with the process said.

U.S. intelligence agencies compile instances of potential violations of the laws of armed conflict by both sides in Gaza as part of a biweekly report titled the “Gaza Crisis Potential Wrongful Acts Summary,” outlining specific incidents and trends related to the war, one of the people familiar with the process said.

Israeli military spokesman Rear Adm. Daniel Hagari said in a press briefing Tuesday that in his 30 years in Israel’s military, the level of intelligence and military cooperation between Israel and the U.S. has never been higher.

“We are experiencing unprecedented levels of intelligence coordination,” he said.

Israeli officials declined to comment on specifics of the intelligence-sharing arrangement.

American spy agencies’ support to Israel is aimed mainly at helping locate the leaders of Hamas’s military wing, finding hostages held by the group and watching Israel’s borders, U.S. officials and others familiar with the issue said. The U.S. shares what is known as raw intelligence, such as live video feeds from intelligence-gathering drones over Gaza, with Israeli security agencies, they said.

The U.S. doesn’t share intelligence specifically intended for ground or airstrike operations in Israel’s military campaign in Gaza, the people familiar with the issue said.

“Our intelligence sharing is focused on hostage-recovery efforts and preventing future incursions into Israel. That includes monitoring mobilization or movement near the border,” an administration official said.

U.S. officials familiar with the October secret memorandum said that Israel is required to ensure that U.S. intelligence isn’t used in ways that cause unacceptable civilian casualties or damage to civilian infrastructure.

Palestinians inspect the site of an Israeli strike on a residential building, amid the ongoing conflict between Israel and Hamas, at Nuseirat refugee camp in central Gaza Strip, March 20, 2024. REUTERS/Ramadan Abed

However, Israel is responsible for certifying its own compliance, and in some cases does so orally, officials said. In addition, they said, it is hard to know how U.S.-provided intelligence is used once it is combined with Israel’s own data.

“Israel provides assurances that operations making use of U.S. intelligence are conducted in a manner consistent with international law, including the Law of Armed Conflict, which calls for the protection of civilians,” a senior U.S. intelligence official said.

When Washington shares intelligence with allies, it first assesses what a partner could do with that information—such as conduct a strike—and decides whether it would be legal for the U.S. to do the same. Based on that determination, the U.S. may ask for additional assurances from the ally on what it would do with the intelligence before sharing it.

“We cannot provide actionable information that could lead to lethal consequences by a country unless we ourselves are authorized to conduct the same activity,” said Douglas London , a retired CIA operations officer and nonresident scholar at the Middle East Institute.

The House Intelligence Committee’s Republican chairman, Michael Turner of Ohio, said in December that the U.S. was being cautious in sharing intelligence on Hamas’s leadership and filling gaps in Israel’s intelligence collection.

“We are being selective as to the information that’s being provided,” Turner said on CBS’s “Face the Nation.”

But Sarah Yager , Washington director of New York-based nonprofit Human Rights Watch said the intelligence-sharing arrangement has little in the way of rules and restrictions and “essentially opens up the entire U.S. vault.”

Separately, the administration is weighing assurances from Israel that U.S.-provided weapons are used in accordance with humanitarian law and isn’t blocking U.S. or U.S.-supported humanitarian aid deliveries, U.S. officials said.

Israel earlier in March provided those assurances, which are required to keep U.S. weapons flowing to the country, they said.

Human Rights Watch and Oxfam, a British charity, argued in a March 19 memorandum to the U.S. government that those assurances are “not credible” and said arms transfers should be suspended immediately.

Write to Warren P. Strobel at Warren.Strobel@wsj.com and Nancy A. Youssef at nancy.youssef@wsj.com