File Photo: Israeli soldiers take part in offensive operations near the border with Lebanon. AFP
The four reservists, all from the same battalion, "fell in combat" on Sunday, the military said without giving further details.
Israel and Hezbollah agreed to a truce after nearly a year of war on 27 November.
As part of the deal, Israeli troops will remain in southern Lebanon for 60 days while the Lebanese army deploys to the area.
Under the agreement, based on a UN Security Council resolution that ended the last Israel-Lebanon war, peacekeepers and the Lebanese army should be the only armed groups in the south.
Starting hours into the agreement, Israel has carried tens out airstrikes and drone attacks on targets inside Lebanon in violation of the truce deal, killing and wounding dozens of Lebanese civilians.
Hezbollah retaliated to Israeli violations on one occasion.
The deaths of four Israeli soldiers bring to 56 the number of Israeli soldiers killed in southern Lebanon since the military launched a ground offensive in late September.
Israeli Prime Minister Benjamin Netanyahu said in a statement that he shared his "deepest condolences" with the families of the soldiers.
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