The army said the arrests were linked to other detentions announced earlier this week.
It added that as military intelligence was investigating that case they got information that a new rocket attack was being planned.
The army said troops raided an apartment near the southern port city of Sidon and seized some of the rockets and the launchers and detained several people who were involved in the operation.
It said they were referred to judicial authorities.
Authorities on Wednesday detained several people, including a number of Palestinians, who were allegedly involved in firing rockets toward Israel in two separate attacks in late March that triggered intense Israeli air strikes on parts of Lebanon.
Lebanon's Hezbollah group denied at the time that it was behind the firing of rockets.
Meanwhile on Sunday, a series of Israeli strikes in southern Lebanon killed two people, the Lebanese Civil Defence said in a statement.
The Israeli army said in a statement that it killed Hussein Ali Nasr, whom it described as the deputy head of Hezbollah's Unit 4400.
Israel said Nasr helped smuggle weapons and funds into Lebanon via "Iranian operatives" including through Beirut airport.
In a separate incident, three Lebanese soldiers were killed after ammunition a Lebanese army vehicle was carrying exploded, the army said in a statement.
The circumstances in which the explosion happened were unclear.
Since a November ceasefire ended a 14-month war between Israel and Hezbollah, Israeli air strikes have killed scores of people in Lebanon including civilians and Hezbollah members.
Israel says it is targeting Hezbollah holdouts in southern Lebanon.
Hezbollah leader Naim Kassem said on Friday that its fighters will not disarm as long as Israeli troops remain in southern Lebanon and the Israeli air force regularly violates Lebanese air space.
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