A halt to the fighting in Lebanon is a condition for starting 60 days of US-Iranian talks to resolve disputes over Iran's nuclear program and other thorny issues key to forging a more durable deal to reopen the Strait of Hormuz and stabilise global oil supplies.
It was not clear when those talks might get under way.
Wednesday's interim US-Iran deal requires both countries and their allies to stop military operations on all fronts, including in Lebanon.
But Israel, left out of the talks, says it is not party to the deal, and will keep its forces in the Lebanese territory it occupies.
A US official had said the truce took effect on Friday afternoon, and Israeli and Hezbollah sources confirmed the agreement to Reuters.
Lebanon's state news agency NNA said Israeli warplanes and drones had on Saturday struck locations across southern Lebanon and the Bekaa Valley, both strongholds of Hezbollah.
An Israeli military official said Hezbollah had fired more than 50 projectiles at Israeli forces in southern Lebanon overnight, and that Israel had attacked what it described as Hezbollah targets in response.
Hezbollah did not immediately claim responsibility. But a senior Hezbollah official told Reuters the group would not allow Israeli forces freedom of movement in Lebanese territory, nor accept a return to the situation that existed before March 2.
Lebanon was sucked into the regional war when Hezbollah attacked Israel after it and its ally, the US, began their war on Iran and Israel responded with an offensive against Hezbollah that included invading south Lebanon.
One of the deadliest Israeli strikes on Saturday hit a three-storey residential building in the Tyre district, killing a father, a mother and their two children, a town official said.
The Lebanese army said an Israeli strike had also killed a soldier.
Lebanon's health ministry says 3912 people have been killed in Israeli attacks since March 2, while Israel says at least 32 Israeli soldiers and four civilians have been killed.
As the fighting raged, it was unclear if any substantive talks would get under way soon between the US and Iran to turn interim a 14-point pact into a lasting deal to end the war that the US and Israel launched on February 28.
Mohsin Naqvi, interior minister of Pakistan, which has been mediating in the conflict, was in Tehran for talks with Foreign Minister Abbas Araqchi, Iran's foreign ministry said.
US Vice-President JD Vance had cancelled plans to head to Switzerland for talks with Iran, which Bern says it is ready to facilitate, as tension between Israel and Hezbollah rose.
The White House would not confirm reports that US President Donald Trump's envoy Steve Witkoff and Trump's son-in-law Jared Kushner still planned to meet Iranian officials in Switzerland.
The Iran war has killed at least 8000 people, mostly in Iran and Lebanon, and has pushed up energy prices, stoking inflation worldwide.
The interim deal foresees relief for Iran from economic sanctions, the unfreezing of assets worth tens of billions of dollars and immediate US waivers for its exports of oil.
It also provides for a $US300 billion ($A428 billion) reconstruction fund for Iran and other financial incentives.
Trump again defended the deal after criticism in Washington, including some from Republican allies who question whether he conceded too much to end an unpopular war ahead of midterm elections in November.
"The War has diminished Iran!" Trump wrote on social media, adding, "We didn't meet out of desperation, Iran did. They are FINISHED! We'll play out the 60 days. They get no money, not 10 cents!"
