Israel, bent on halting any transfer of weapons to Lebanon's Hezbollah, has bombarded a position of the powerful Shiite group on the Lebanese-Syrian border, Lebanese sources said on Tuesday.
"Two Israeli raids hit a Hezbollah target on the border of Lebanon and Syria" on Monday night, a Lebanese security source told AFP.
Lebanon's National News Agency said the raids struck outside the border town of Nabi Sheet, a Hezbollah bastion where its fighters are suspected of maintaining a weapons store and training camp.
Residents told AFP they saw flares light up the sky ahead of the raids, which shook their houses.
They said they heard planes flying low and that the target appeared to be a Hezbollah position in the nearby mountains.
There was no official comment on the raids from Hezbollah, the Lebanese government or Syria, although the army said there had been Israeli violations of Lebanese airspace.
Hezbollah is an arch-enemy of Israel, and has sent thousands of fighters across the border to aid Syrian President Bashar al-Assad's regime as it battles Sunni-led rebels.
Syria has long provided arms and other aid to Hezbollah, and served as a conduit for Iranian military aid to the movement, which battled Israel to a bloody stalemate in a brief 2006 war.
Israeli officials from Prime Minister Benjamin Netanyahu down refrained from commenting specifically on Monday night's reported raid although they confirmed a policy of interdiction of suspected arms deliveries to Hezbollah.
"We are doing everything that is necessary in order to defend the security of Israel," Netanyahu said on Tuesday.
"We will not say what we're doing or what we're not doing."
The commander of Haifa naval base on Israel's northern coast told the Haaretz newspaper that Hezbollah was trying to procure sophisticated arms.
"The major players in the arena are active and relevant. Hezbollah has not stopped for a second to try and get its hands on advanced weaponry," Brigadier General Eli Sharvit was quoted as saying.
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- Hezbollah 'made itself target' -
Lebanon's Al-Akhbar newspaper, which is close to Hezbollah, said the raids took place inside Syria, adding that "the nature of the target is unclear."
But a Lebanese army source told AFP: "The raids most likely took place on Lebanese territory, but we cannot be completely sure because the borders in that area are not well defined."
Waddah Charara, a sociology professor and author of "The State of Hezbollah," said the raids would mark an important turning point if they took place inside Lebanon.
"It would be the first Israeli strike against Hezbollah in Lebanon" since the 2006 war, Charara told AFP.
He said Hezbollah had helped "legitimise these raids in Lebanon" by involving itself in the Syrian conflict.
"The moment that it violated that national boundary, and became a regional force subordinate to Syrian interests, it became a target for Israel and no longer enjoyed the protection accorded by the 'nationalist' character of its actions."
Hezbollah enjoyed widespread support in Lebanon during the 2006 conflict with Israel, but its popularity has diminished in recent years, and its decision to intervene in the Syrian conflict is controversial.
Now, "Israel can attack Lebanon because it knows there will be no reaction at the national level," said Charara.
Inside Syria, meanwhile, fighting raged in flashpoints across the country, with Hezbollah fighters joining troops battling rebels on key fronts, chiefly around Damascus and second city Aleppo.
In east Aleppo, government forces advanced into the outskirts of the Tariq al-Bab district in fighting that killed 17 rebels, the Syrian Observatory for Human Rights said
The advance marked the first time the army had penetrated the area since late 2012, when several months of fighting left Aleppo divided between a government-held west and rebel-held east.
An estimated 140,000 people have been killed since the conflict erupted in March 2011. Nearly 2.5 million more have registered as refugees in neighbouring countries, according to the UN High Commissioner for Refugees.