Israel and Hezbollah agreed to renew a fragile ceasefire in Lebanon on Friday after 24 hours of intense violence that posed an early challenge to the new agreement between the US and Iran to end their conflict.

A meeting that was scheduled to take place on Friday between Washington and Tehran in Switzerland to discuss implementation of the new deal was cancelled when Hezbollah killed four Israeli soldiers and Israel carried out a wave of retaliatory airstrikes in southern Lebanon and the Bekaa valley that killed at least 47 people.

The talks were to have begun in the Swiss village of Obbürgen two days after the signing of a memorandum of understanding (MoU) that opened a 60-day window to negotiate a permanent understanding over Iran’s nuclear programme while getting oil traffic moving through the strait of Hormuz.

The MoU called for an end to hostilities on all fronts, including in Lebanon.Iran’s chief negotiator, Mohammad Bagher Ghalibaf, warned on Friday against any breach of the agreement, threatening a “decisive response … to the enemy”.

The flaring violence and diplomatic back-and-forth over the planned talks added to the uncertainty over ​whether a definitive end could be found to a regional war that has killed at least ‌7,000 people, sent energy prices soaring and threatened global economic chaos.

Donald Trump again defended the deal after criticism in Washington, including from some of his Republican allies in Congress who have questioned whether he conceded too much to end a war unpopular with most Americans before November’s midterm elections.

“The War has diminished Iran!” he wrote in social media posts on Friday. “We didn’t meet out of desperation, Iran did. They are FINISHED! We’ll play out the 60 days. They get no money, not ten cents!”

Lebanon has emerged as a flashpoint that could upend Trump’s efforts to extricate the US from the war, frustrating the president, who has lashed out at Israel and its prime minister, Benjamin Netanyahu.

The latest clashes between Israel and Hezbollah, which has close ties with Tehran, were the most violent since the ceasefire was established. Hezbollah targeted Israeli forces near the city of Nabatieh, in southern Lebanon, with several salvoes of rocket fire and drones overnight after intermittent Israeli shelling throughout Thursday.

Israel responded with a wave of airstrikes on the city and surrounding towns against what it said were Hezbollah targets, leaving at least 18 people dead and 33 wounded, according to Lebanon’s ministry of health.

By evening, the clashes appeared to have ended. “If Hezbollah does not attack us, then for us it is not a time of war,” an Israeli official said late on Friday. Two Hezbollah sources confirmed a new ceasefire to Reuters.

Many Israeli commentators believe Iran will be strengthened by the deal agreed by Trump earlier this week, and the killing of Israeli soldiers by Hezbollah prompted fury.

Netanyahu, who promised the joint US-Israeli war against Iran would lead to regime change in Tehran, has faced fierce domestic criticism this week. His office issued a statement saying Israel would not tolerate attacks on its soldiers or territory, and would “exact a very heavy price from Hezbollah for these attacks”.

“Israel will remain in the security zone in southern Lebanon for as long as necessary for the protection of the communities of the north,” the statement said.

Netanyahu faces elections within months and is under pressure from political rivals. Israel’s far-right national security minister, Itamar Ben-Gvir, said “all of Lebanon must burn”. “With all due respect to the Americans, Israel must make it clear to the entire world that the blood of our sons and the security of our citizens are not up for bargaining,” he said in a statement.

The cancellation of the talks between Iran and the US on Friday came so abruptly that the staff of the US vice-president, JD Vance, and a small pack of journalists had gathered at Joint Base Andrews outside Washington in anticipation of the trip. Dozens of White House officials, advance staffers and media were already in Switzerland to prepare for Vance’s arrival.

Iran’s supreme leader, Ayatollah Mojtaba Khamenei, said on Thursday that he had approved the MoU despite reservations, while the US officially lifted a blockade of Iranian ports.

Before the talks were cancelled, Iran’s semi-official Tasnim news agency said Iranian negotiators needed ⁠to see signs of implementation of the interim agreement from the US before the next rounds of peace talks could begin, and that there was no confirmation that Tehran’s delegation would travel to Geneva.

Israel, which was not included in the peace talks and has distanced itself from the US-Iran agreement, has accused Hezbollah of violating the ceasefire, an accusation the group has thrown back at Israel.

Fighting began in Lebanon on 2 March when Hezbollah launched rockets at Israel in what it said was revenge for the killing of Iran’s supreme leader by the US and Israel in the opening wave of attacks of the most recent war. The subsequent Israeli invasion of southern Lebanon and bombing campaign has left more than 3,900 people dead. Hezbollah has killed at least 32 Israeli soldiers in Lebanon and three Israeli civilians.

On Thursday, Israel announced a “security zone” in southern Lebanon, which comprises hundreds of square miles of territory. Lebanese officials have demanded a complete withdrawal of Israeli forces, something Iran said was required by the MoU.

Vance said Israel needed to respect the peace process.

US forces have lifted their naval blockade of Iranian ports that prevented ships from sailing to or from the country, the US military said on Thursday, noting that its warships would “remain in the general area”.

Activity remained muted in the strait of Hormuz, the strategic bottleneck for energy shipments that Iran blockaded during the conflict.