Budapest, Hungary - Vice President JD Vance on Wednesday urged Iran not to let the fragile ceasefire deal fall apart over Israel's attacks on Lebanon, days before he is due to lead talks with Tehran in Pakistan.

Iran's president said a truce in Lebanon was a key condition for ending the Middle East war, Vance said he believed there had been a "legitimate misunderstanding".

"I think the Iranians thought that the ceasefire included Lebanon, and it just didn't. We never made that promise," Vance said as he left Hungary, where he was visiting to boost the re-election chances of far-right Prime Minister Viktor Orban.

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"If Iran wants to let this negotiation fall apart... over Lebanon, which has nothing to do with them, and which the United States never once said was part of the ceasefire, that's ultimately their choice."

A day after Washington and Tehran agreed a two-week truce, Israel carried out its heaviest strikes on Lebanon since Iran-backed militant group Hezbollah joined the war in early March.

The strikes killed at least 112 people and wounded hundreds, according to the Lebanese Health Ministry.

But Vance claimed that the Israelis had offered to show restraint.

"The Israelis... have actually offered to be, frankly, to check themselves a little bit in Lebanon, because they want to make sure that our negotiation is successful," Vance said.

The US vice president warned that President Donald Trump expected Iran to keep its promise to open the Strait of Hormuz to oil traffic.

"Frankly, if they break their end of the bargain, then they're going to see some serious consequences," Vance added.

Vance is due to lead a negotiating team, including special envoy Steve Witkoff and Trump's son-in-law Jared Kushne, to Islamabad for "in person" talks with Iran on Saturday, the White House said earlier.