Israeli soldiers were scouring the northern part of the country Monday after reports that a rocket was fired toward the area from southern Lebanon.
Lebanese and Israeli media, citing security sources in both countries, reported that residents in the Marjayoun area of Lebanon, about six miles from the Israeli border, heard either the launch or the sound of a missile streaking through the air.
An IDF spokesman said residents of Metula, Israel, then heard an explosion, according to The Jerusalem Post.
"We haven't opened the bomb shelters, but we are ready," the newspaper quoted an IDF spokesperson as saying.
It was not clear who fired the rocket or mortar.
IDF teams found no sign of an exploded rocket or other projectile Sunday night and were searching again Monday, Reuters reported.
The incident comes as tensions from Syria have boiled over into Lebanon, where the militant group Hezbollah has vowed to support Syrian President Bashar Assad in the two-year civil war that has claimed more than 70,000 lives, according to U.N. estimates.
Israel, which keeps a wary eye on Hezbollah, has launched airstrikes in Syria that it says were aimed at the militant group and not the Syrian government.
Israel has repeatedly said that it would not allow long-time enemy Hezbollah to obtain sophisticated weapons.
There are also fears that Hezbollah’s backing of Assad could further inflame sectarian violence in Lebanon.
On Sunday, two missiles struck a Shiite Muslim area in southern Beirut that is considered a Hezbollah stronghold. Sunni Muslims in Lebanon tend to support the rebel forces fighting Assad.
NBC News' Lawahez Jabari and Reuters contributed to this report.