Israel's flag flew over the medieval fortress on Beaufort in Lebanon on Sunday as it warned Lebanese civilians to evacuate a large area of the south of the country ahead of stepped up ground operations.

Shelling was audible and smoke rose from the surrounding area as the invading army's banner was seen by AFP above the castle, which Israeli forces famously used as a base during their previous two-decade long occupation.

The Israeli army announced Sunday that one of its soldiers had been killed the previous day by a Hezbollah explosive drone in southern Lebanon, bringing to 25 the number of Israeli military deaths since early March.

The Israeli military warned Lebanese civilians living south of the Zahrani river to evacuate the region Sunday, warning that it was stepping up operations against Hezbollah.

Prime Minister Nawaf Salam has denounced what he called a dangerous Israeli escalation in the south, urging an immediate ceasefire and insisting that a "scorched-earth policy" would not ensure Israel's security.

In a televised address, Salam also defended his government's direct negotiations with Israel -- which Iran-backed Hezbollah opposes -- saying that the talks were the "least costly path" for Lebanon.

U.S. President Donald Trump said he had secured guarantees from Iran that it would not develop nuclear weapons, as reports emerged he had sent a tougher peace proposal back to Tehran.

Any tweaks to the proposal could prolong even further an agreement to formally end the Middle East war and open the Strait of Hormuz maritime route after weeks of efforts to secure a deal despite fractious rhetoric and the occasional flare up of armed conflict.

Fifteen children have been killed in Lebanon and 62 injured over the last seven days, the United Nations said Friday, despite the ceasefire between Israel and Hezbollah.

Lebanon is seeking an international force to replace a decades-long United Nations peacekeeping mission whose mandate ends this year following U.S. and Israeli pressure, even as the latest Israel-Hezbollah war continues.

Military officials from Israel and Lebanon held "productive" talks in Washington on Friday, a U.S. official said, adding that the meeting will complement upcoming diplomatic discussions.

Hezbollah said on Saturday it fired rockets at the northern Israeli settlement of Kiryat Shmona, as exchanges of fire between the two sides have intensified despite Lebanon-Israel negotiations.

Israel's military issued evacuation warnings on Saturday for residents of seven villages in southern Lebanon, after Israeli Prime Minister Benjamin Netanyahu said Israeli forces had pushed deeper into the country.