A rocket was fired from the southern Lebanese town of Marjayoun towards Israel Sunday.
It is unclear if the rocket landed on Israeli territory but local residents report hearing the blast.
"An explosion was heard. Soldiers are searching the area. The cause is still being investigated," an Israeli military spokeswoman said.
The Israeli Defense Forces have begun searching for the rocket's remains.
Earlier Sunday, two rockets were fired towards a Hezbollah-dominated neighborhood in southern Beirut.
The blast injured five people but it was unclear who was being targeted.
On Monday, Lebanese officials, denying witness reports, said a rocket had not been fired from south Lebanon towards Israel, Hezbollah-affiliated Al-Manar website reported.
A senior Lebanese military official said on the 'Voice of Lebanon' radio that "no rocket was fired on Israel."
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The rockets landed just hours after Hezbollah's leader Hassan Nasrallah declared further support for Syrian leader Bashar al-Assad.
The speeched marked the 13th anniversary of the withdrawal of Israeli forces from Lebanon.
Whether it likes it or not, Lebanon has been increasingly involved in the war raging in neighboring Syria.
Scores have been killed in clashes between Alawites and Sunnis in the northern city of Tripoli.
The Shiite militant group Hezbollah is openly fighting alonside Assad's forces in Syria, battling mainly Sunni rebels.
Israel has also seen violence on its border with Syria, while attacking alleged weapons convoys heading to Hezbollah traveling through that country.
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