Word of the ceasefire came from two regional officials and a U.S. official. The truce was mediated by Qatar, the U.S. and Iran, the regional officials said.
Israel and Hezbollah did not immediately comment.
THIS IS A BREAKING NEWS UPDATE. AP's earlier story follows below.
JERUSALEM (AP) — Talks between the U.S. and Iran were called off Friday after intense fighting between Israel and Hezbollah in southern Lebanon, officials said, raising questions about an initial agreement to end the war in Iran.
Iranian officials didn't travel as planned to Switzerland, insisting that the fighting in Lebanon must stop before the talks can take place, according to three regional officials and a fourth person familiar with the matter who spoke on condition of anonymity to discuss sensitive conversations behind the scenes. U.S. Vice President JD Vance also postponed his trip.
Israel's military struck targets in southern and eastern Lebanon overnight, and Hezbollah reported intense fighting. Lebanon's Health Ministry said at least 21 people were killed, and Israel said four soldiers died.
The conflict between Israel and the Iran-backed militant group is the most precarious part of the Iran deal. Neither Israel nor the militant group signed the agreement — but it is supposed to end their fighting, and Iran has signaled its willingness to risk renewed war in the region for the sake of its interests in Lebanon and its most important regional ally.
The interim deal has halted hostilities in Iran and the Gulf and reopened the Strait of Hormuz, after Iranian attacks and threats all but stopped the flow of oil and natural gas through the waterway, creating a global energy crisis.
But future talks are supposed to bring about a permanent end to the conflict, including addressing how to restrict Iran's nuclear program — the core issue over which Israel and the U.S. went to war on Feb. 28.
The Israeli military said four soldiers, including a lieutenant colonel, were killed in an attack on a tank in a village near the southern Lebanese city of Nabatiyeh. An explosive drone attack wounded another five, it added.
Israel then launched multiple strikes against "Hezbollah infrastructure sites" in Nabatiyeh and other areas, according to a military statement, which accused the militant group of "blatant ceasefire violations."
Later, the military said it also struck targets in the Bekaa Valley in eastern Lebanon, with Lebanese media saying the village of Douris was hit.
"Israel will not tolerate attacks on our soldiers or on our territory, and it will exact a very heavy price from Hezbollah for these attacks," Israeli Prime Minister Benjamin Netanyahu said in a statement.
Hezbollah acknowledged targeting Israeli tanks and said its attacks were in response to what it called Israel's own violation of the ceasefire. It said the attacks came after Israeli forces attempted to reach the northern side of Ali al-Taher hilltop, a strategic point that overlooks Nabatiyeh and that Israeli troops have been trying to capture.
In southern Lebanon, many were forced to flee their villages.
"The situation is lawless, we couldn't stay," said Mustafa Zain, who was with his six daughters in a pickup truck.
Beyond the fighting, Israel's occupation of large swaths of southern Lebanon is also a sticking point. Iran insists Israel must withdraw, but Netanyahu has said that forces would remain in a "security zone" of southern Lebanon as long as "Israel's security needs require it."
Israel's actions have created a rift between Israel and the U.S., with Trump becoming increasingly critical of his close ally Netanyahu, who is also facing increasing criticism at home.
Iranian officials balked at starting the talks with Vance in Switzerland because of the Israeli action in Lebanon, according to the person familiar with the White House and Iranian positions.
It was conveyed to Iran that Israel is ready to move on, and it's up to Hezbollah to stop carrying out attacks, the person added.
Earlier, the White House blamed logistical issues when Vance put off his trip.
Two other regional officials, also speaking on condition of anonymity to discuss the closed-door talks, described Pakistan as being "stunned" by Iran's decision not to go to the talks.
Oil tankers began freely moving through the Strait of Hormuz this week after months of being largely unable to use the critical channel. More than 12.5 million barrels of oil were shipped through the waterway on Wednesday night, the U.S. said.
Still, it is expected to take weeks or months for the normal flow of oil and gas to resume, even if traffic fully resumes.
The interim deal lays out that passage through the strait should be free for 60 days — as it was before the war. But the new Iranian authority charged with overseeing the waterway issued guidance Friday calling on ships to register with it — signaling Tehran likely intends to start charging.
The Persian Gulf Strait Authority said Friday that "during the 60-day period, tariffs for security, safety and environmental services, as well as related Iranian insurance, will not be collected from shipowners and will be borne by the government of the Islamic Republic of Iran."
The discussions in Switzerland are expected to focus on Iran's nuclear program. Tehran maintains it is peaceful, though it has highly enriched uranium that could be used to build multiple atomic bombs, should it choose to do so, according to the International Atomic Energy Agency.
Those talks are expected to be extremely difficult. The 2015 nuclear deal, which Trump scrapped during his first term, took more than 18 months to negotiate.
The interim deal gives negotiators 60 days to come up with a nuclear agreement, but that can be extended. It outlines lucrative incentives if Iran does reach a new agreement, including the eventual lifting of all international sanctions and a $300 billion fund for postwar reconstruction.
Already Iran has won some concessions. Following the signing of the interim deal, the U.S. lifted its blockade of Iran's ports and is allowing it to sell its oil freely. The deal also calls for Iran's assets to be unfrozen — though it's not clear how quickly.