An air strike on the road linking the city of Nabatiyeh with the town of Marjayoun occurred in the morning killing a brigadier general, a captain and another soldier, the army said without immediately releasing their names.
Another air strike on the southern village of Saksakiyah killed six people and wounded four, state-run National News Agency said.
"The continued, deliberate and repeated Israeli aggression against Lebanon, its people and its army only strengthens our resolve, faith and determination," the army said in its statement.
It said Israel's attacks aimed to thwart all efforts "to reach a solution that would restore stability, establish a comprehensive ceasefire and lead to the Israeli withdrawal from the occupied Lebanese territories".
There was no immediate comment from the Israeli military on the air strike that killed the troops.
The latest declared ceasefire came about through US-brokered talks between Israel and Lebanon's government, which accuses Hezbollah of dragging the country into war and had made efforts to disarm it before the latest hostilities.
The Lebanese militant group has refused the truce.
The air strikes came a day after Lebanon's president and prime minister criticised Iran for opposing the latest ceasefire deal between the Lebanese government and Israel, saying their country should not be used by Tehran as a "bargaining chip" in its talks with Washington.
Iranian Foreign Minister Abbas Araghchi responded in a post on X on Saturday by saying that after President Joseph Aoun's comments "one would think it's Iran that has occupied a fifth of Lebanon, displaced a quarter of Lebanese and is bombing his country on daily basis".
"Had Lebanon been a bargaining chip for Iran, we'd have a deal long ago. Save Lebanon from your real foe, Mr President," Araghchi said in reference to Israel.
The war began on March 2 when Hezbollah fired rockets at northern Israel, two days after Israel and the US began their attacks on Iran.
Israel has since launched a ground invasion of Lebanon and carried out wide attacks that have displaced more than one million people.
Israeli troops have seized about a fifth of Lebanon, pushing further into the country's south than at any time since the end of Israel's 1982-2000 occupation.
More than 3500 people have been killed in Lebanon since the war began.
The fighting has killed at least 29 Israeli soldiers and three civilians.
