An Israeli Air Force F-15 Strike Eagle flies in formation with a US Air Force B-1B Lancer over Israel. Photo for illustrative purpose Image Credit: AP file

Jerusalem: A loud sound in Beirut probably was caused by Israeli warplanes flying over the Lebanese capital on Friday evening, according to a security source and a Reuters witness.

Israeli planes were flying low over Beirut at the time, the security source said. A Reuters witness reported two jets in the skies over the capital.

Earlier in the day, Israel's military said its missile defences had been triggered by an unmanned aircraft that crossed into Israel from Lebanon.

Moments earlier air raid sirens sounded in the Galilee region of northern Israel, warning residents to take cover. There were no immediate reports of injuries or damage.

"Iron Dome interceptors were launched according to protocol and fighter jets were scrambled to patrol the area. No special instructions for civilians in the area have been issued," the military said in a statement.

Hours later, investigations concluded the drone managed to return to Lebanon, the Israeli military said in a statement, stopping short of blaming Lebanon's Hezbollah militant group on launching the drone.

In Lebanon, Hezbollah issued a statement saying it had it sent the "Hassan" drone inside Israel. It claimed the drone toured the targeted area for 40 minutes on a "reconnaissance mission that extended along seventy kilometers" inside Israel.

The move comes just a day after Israel shot down what it said was another Hezbollah drone. Neither Lebanon nor Hezbollah gave immediate comment.

Neighbours Lebanon and Israel are technically in a state of war and drones have become a regular feature of their heavily guarded border.

In January, Israeli security sources claimed that drones captured after being flown across the frontier from Lebanon have provided insight into the growing aerial surveillance capabilities of Hezbollah, an organisation backed by Israel’s nemesis Iran.

The Israeli army, in a statement on Thursday, said “troops downed a drone belonging to the Hezbollah terrorist organisation that crossed from Lebanon into Israeli airspace.”

The Israeli army “will continue to operate in order to prevent any attempt to violate Israeli sovereignty,” it added.

In July 2006, Hezbollah captured two Israeli soldiers, sparking a 33-day war with Israel that killed 1,200 people in Lebanon and 160 Israelis, mostly soldiers.

It ended with a UN-backed ceasefire that saw the Lebanese army deploy along border areas.