The US and Iran traded strikes hours before the burial of the late supreme leader Ayatollah Ali Khamenei on Thursday, with 17 people killed by US strikes while Tehran launched attacks against American bases in the region, straining an already shaky ceasefire.

The tit-for-tat strikes were the largest since Tehran and Washington signed a memorandum of understanding (MoU) on 17 June aimed at extending the ceasefire and giving space for negotiations for a permanent truce.

Sirens sounded at least three times in Bahrain, where the US navy’s fifth fleet is headquartered, while Iranian missiles also targeted Kuwait and Qatar. Iran’s Islamic Revolutionary Guard Corps said it fired 10 ballistic missiles at Jordan’s Azraq military base on Thursday afternoon, which the US air force uses. There were no immediate reports of any damage in Jordan or the Gulf.

In Iran, officials said strikes targeted the perimeter of Iran’s only civilian nuclear plant in Bushehr province, an area where the UN’s nuclear watchdog has previously warned that attacks could “pose a very real danger to nuclear safety”.

“Several areas in Bushehr province were targeted today, including the perimeter of the nuclear power plant, a military base in the town of Choghadak and a fishing pier in the south of the province,” said Ehsan Jahanian, the deputy governor of Bushehr, adding there were no reports of casualties so far.

The attacks came hours after Donald Trump said the MoU was “over” because of Iranian attacks on ships in the strait of Hormuz. After the strikes, the US president posted videos of explosions in Iran and threatened the country once again.

“This is in retribution for yesterday’s bombing of ships by Iran. If it happens again, it will get much worse!” Trump wrote on Truth Social. Hours before, he had promised strikes would not lead to long-term fighting but would be “very fast”.

His comments and the exchange of fire prompted worries that the ceasefire could break down and raised concerns about the long-term prospects of negotiations. Significant gaps remain between the two countries over issues such as Iran’s control over the strait, as well as inspections of nuclear facilities.

Back-and-forth attacks have happened since the MoU was signed, but Thursday’s strikes were the most intense in weeks.

They came as Iran prepared to bury Khamenei in his home town of Mashhad. A fighter jet escorted the plane carrying Khamenei’s coffin amid the tense security situation. Crowds of people gathered for the occasion, some holding banners promising vengeance against the US.

Observers waited to see if Iran’s new supreme leader, Mojtaba Khamenei, would attend the burial. He was wounded in the same series of strikes that killed his father and has since only communicated through written statements.

The US military said it hit about 90 targets in Iran, showing footage of strikes on missile launchers and a runway. It said the attacks were meant to degrade Iran’s capacity to “threaten freedom of navigation” in the strait of Hormuz, a critical choke point for about 20% of the world’s oil and gas.

Iran accused the US of war crimes after it said two bridges in the eastern provinces leading to the city of Mashhad were targeted. The bridges constitute key infrastructure for Iran’s cross-border trade with China, which has dramatically increased since the start of the war.

Trump has repeatedly threatened to hit bridges, power plants and other civilian infrastructure in Iran. Targeting civilian infrastructure if it is not a military objective could amount to a war crime.

Iranian state media also reported explosions in several cities, including Bushehr, which houses Iran’s nuclear power plant complex. At least three people were killed in Iran’s south-western Khuzestan province, while a firefighter was killed in an airport in the south-eastern city of Iranshahr. Nine members of Iran’s military also died in strikes on Wednesday.

The US attacked Iran after Iran struck three ships in the strait of Hormuz on Tuesday. Iran stopped virtually all shipping out of the strait during the war, sending global energy prices soaring and putting pressure on Trump domestically before midterm elections.

The MoU calls for the reopening of the strait to commercial shipping for 60 days. Iran says it wants to charge fees to ships transiting through the strait, conflicting with the US, which says it is an international waterway and should not have tolls.

Iran continues to view its control over the strait as an important source of leverage in its negotiations with the US, while Trump appears to view strikes on Iran as a way of increasing pressure on Tehran.

Mohammad Bagher Ghalibaf, a senior Iranian negotiator and parliament speaker, said US pressure would not lead anywhere. “America still hasn’t learned that bullying and breaking promises are no longer cost-free,” he said in a post on X. “Let me put it plainly: If you strike, you’ll get hit.”

Mediators attempted to de-escalate tensions between the US and Iran in an effort to salvage negotiations. The Qatari prime minister, Sheikh Mohammed bin Abdulrahman Al Thani, a key intermediary between the countries, spoke to Iran’s foreign minister, Abbas Araghchi, on Thursday, condemning Tehran’s strikes on ships in the strait.

“His excellency stressed that such actions would undermine trust, threaten international maritime security, and harm efforts to consolidate regional security and stability,” a statement from the Qatari foreign ministry said.

Negotiations towards reaching a final deal were intended to start after the conclusion on Thursday of Khamenei’s seven-day funeral. The two days of strikes meant talks would be held amid escalating tensions

Trump had said on Wednesday that negotiators were “wasting their time”. Iran’s deputy foreign minister, Kazem Gharibabadi, shot back at Trump, calling his comments “a confession to the failure of a policy that has been based on force, sanctions and threats for years and could not bring the Iranian nation to its knees”.

Gharibabadi wrote on X: “With the criminal and the murderer Trump, one must speak his own language, apparently understands the language of force better!”

Additional reporting by Patrick Wintour