Western officials say they are braced for a period of increased volatility with Iran as the country prepares to choose a successor to President Ebrahim Raisi , who died in a helicopter crash over the weekend. But they said they don’t expect Tehran to make major foreign-policy shifts.

Iran, where ultimate authority lies with Supreme Leader Ayatollah Ali Khamenei , is likely to stay on its current trajectory, deepening ties with China and Russia , supporting Hamas and other regional militias and pursuing its nuclear program, officials in Washington and European capitals said.

The coming election campaign, set to end in a vote on June 28, could generate momentum in Iran for a more assertive posture in the region, these officials said. The approach of U.S. elections and a possible White House transition could also be seen by Khamenei as an opportunity to push a tougher stance.

A more immediate worry is that Iran might react to threats, real or imagined, that adversaries could try to take advantage of political upheaval as a new president takes office against the backdrop of widespread popular protests in recent years.

U.S. officials say the Biden administration’s fundamental approach to Iran now boils down to keeping open channels of communication to avoid direct conflict or a crisis in the run-up to November’s elections.

“Ayatollah Khamenei and the security bureaucracy will be acutely aware of the risk inherent in any perception of vulnerability,” said  Suzanne Maloney , director of the Foreign Policy program at the Brookings Institution. “I’d expect a skittish, reactive Iran at a time when the temperature is already running high in the region.”

The State Department offered “official condolences” for the death of Raisi and other Iranian officials while reaffirming its support for the Iranian people “and their struggle for human rights and fundamental freedoms.” On Tuesday, U.S. Secretary of State Antony Blinken said during a congressional hearing that “given the horrible acts” Raisi had committed as a judge and as president, the Iranian people were probably better off without him and “we’re certainly not mourning the death.”

Russian President Vladimir Putin was one of the first foreign leaders to phone Iran’s new interim President Mohammad Mokhber to express his condolences on Monday.

Iran had asked Washington and Moscow for help finding Raisi’s helicopter. Russia sent planes, a helicopter and personnel. The U.S. agreed but ultimately wasn’t able to provide that help, which probably would have consisted of satellite reconnaissance, for what the State Department said were “logistical reasons.”

While Iran’s military and foreign policy strategies are framed by Khamenei and his advisers, a new president and his team would have some sway over how these are implemented.

Decision makers in Washington and Europe will look first to see what signals Tehran sends about its potential foreign policy priorities by which presidential candidates it permits to run and who wins, said Michael Singh, a former National Security Council official now at the Washington Institute for Near East Policy, a think tank.

In 2021 for example, the regime banned former parliament speaker Ali Larijani , the front-runner who was seen as more moderate than Raisi, from running.

Last week, senior U.S. and Iranian officials, including a diplomat who has since become Iran’s new acting foreign minister, Ali Bagheri-Kani , held indirect talks in Oman for the first time since January. Iran won’t meet face-to-face with the U.S. so Omani officials shuffle messages between the teams.

The two sides discussed nuclear and regional issues, according to people briefed on discussions, with U.S. officials nudging Tehran to control its production of highly enriched uranium and cooperate with the United Nations atomic agency as a pathway to improved relations.

Bagheri-Kani was due to meet European counterparts this week but the deaths of Raisi and Abdollahian scuttled those plans.

Some Western officials say the elevation of Bagheri-Kani is welcome, seeing Iran’s chief nuclear negotiator, who has personal ties to Khamenei and opposed the 2015 nuclear deal, as now favoring de-escalation of tensions with the West. But it is unclear if he will keep the role under a new team or how much influence he will have in a regime dominated by hard-liners.

The possibility that Iran might edge closer to a nuclear weapon is perhaps the greatest concern among Western officials.

Iran’s nuclear program has advanced significantly in recent years and Tehran has now stockpiled enough fissile material for around three nuclear weapons, experts say. Iran denies it has ever worked on nuclear weapons and U.S. officials say there is no evidence that Iran is trying to build a nuclear weapon.

Talks on reviving the 2015 nuclear deal, which lifted most international sanctions on Tehran in exchange for tight but temporary limits on Iran’s nuclear work, collapsed in 2022 .

In recent months, Iranian officials have suggested that they are close to mastering the ability to build a nuclear weapon and that the fatwa, a religious order, Khamenei issued in 2003 against the use of weapons of mass destruction could be revisited. Any such change, however, could only come from the top leadership.

“We are moving closer to a situation where there is a big, huge question mark about what they are doing and why they are doing it,” International Atomic Energy Agency Director-General Rafael Grossi told the Guardian earlier this month.

Less prone to a shift is Iran’s approach to Gaza. Tehran’s entire political establishment backed Hamas’ fight with Israel.

U.S. intelligence agencies assessed in this year’s annual report on worldwide threats that Iranian leaders “did not orchestrate nor had foreknowledge” of Hamas’ Oct. 7 attacks on Israel. But Khamenei has hailed the attacks, which Israel has said killed about 1,200 Israelis, mostly civilians.

Iranian officials have denounced regional normalization efforts between Israel and Arab states, including Biden administration efforts to establish formal relations between Israel and Saudi Arabia , potentially a major shift in the regional power balance.

Iran’s missile and drone attack on Israel last month marked Tehran’s first direct attack on Israel. It was taken in response to an Israeli strike on Iranian paramilitary officials in Damascus.

Yet after that attack and Israel’s narrow response in central Iran, both sides sought to avoid an escalation of the clash.

Tehran has also sought to avoid direct conflict with the U.S. or pushing Hezbollah to open a new front against Israel from Lebanon. After three U.S. soldiers were killed by a pro-Iranian Iraqi militia in late January, Khamenei personally intervened to prevent further attacks on U.S. forces, according to two Western diplomats.

“That policy is being set up high,” said Ali Vaez , director of the Iran Project and a senior adviser at conflict resolution organization Crisis Group. “That’s why you see a high level of continuity over the years because presidents have come and gone…and the policy towards Iran’s network of nonstate actors in the region has not changed.”

Raisi championed Iran’s turn to the east under his presidency, playing down the importance of relations with the West and giving priority to smoother relations with Iran’s Gulf Arab neighbors and closer ties with Beijing and Moscow.

Most significantly, with the help of Beijing, his government re-established diplomatic ties with Saudi Arabia in 2023, seven years after the two regional rivals severed relations over a series of disputes. Iran became a permanent member of the Russia, China-led Shanghai Cooperation Organization and of the Brics Group.

Yet Iran’s most consequential decisions were made by Iran’s security establishment, experts say, in particular the move to supply drones and drone technology to Russia for its war in Ukraine. U.S. officials are still expecting Tehran to send ballistic missiles to Russia, a step that Washington has warned would produce a volley of joint Western sanctions on Tehran.

“I think that the decision to align strategically with the Kremlin as well as with Beijing…is frankly growing firmer by the year,” said Singh. “I think that the days of Iran hoping for a rapprochement with the West…are over for the foreseeable future.”

Write to Laurence Norman at laurence.norman@wsj.com and Michael R. Gordon at michael.gordon@wsj.com