At least five people died, including four Syrian soldiers and a 15-year-old Lebanese boy, as Syrian troops exchanged fire on Monday with Lebanese soldiers and armed groups in clashes along the border.
The teenager was killed by retaliatory Syrian bombing on the Syrian border village of Qasr, which also destroyed several homes.
The fighting on the border between the Syrian governorate of Homs and Hermel, in Lebanon's Bekaa Valley, was sparked by the killing of three members of the new Syrian Defence Ministry force in a border ambush on Sunday, the sources said. Hermel is a Hezbollah stronghold in the Bekaa Valley, where clans involved in illicit activity also operate.
The escalation has marred recent efforts by the two governments to improve relations since the fall of former Syrian dictator Bashar Al Assad. The clashes pit fighters led by Hayat Tahrir Al Sham (HTS) against forces aligned with Hezbollah, as well as the Lebanese army, whom the authorities in Beirut say has been instructed to respond. HTS, a group formerly linked with Al Qaeda, took power in Damascus after fall of the Assad regime in December.
Lebanon has been among a constellation of Arab countries that have been engaged in diplomacy with the new order in Damascus, in a bid to establish new ground rules between Syria and its neighbours, after decades of volatile relations under the Iran-backed former regime.
An HTS official told The National that the four Syrian soldiers killed on Sunday were on an anti-narcotics mission in Hermel when they were apparently captured by members of one of the many drug groups in the area. A video on social media purportedly showed one of the three soldiers sitting on the ground and being struck by stones, with one hitting him in the head. The HTS official confirmed the authenticity of the footage and said another four soldiers were killed in the border clashes on Monday.

A Hezbollah source told The National that a 15-year-old Lebanese boy was killed by retaliatory Syrian bombing in the border village of Qasr that also destroyed several homes. The clashes began on Sunday when three Syrians crossed the border, the Hezbollah source said. “Lebanese villagers opened fire on them and captured them. The three men died. The villagers are defending their land and this has nothing to do with Hezbollah.”
Footage on pro-Syrian government channels purportedly showed HTS led troops firing rockets at Hezbollah positions. One Syrian tank was hit in the clashes, according to the channels.
The border clashes have prompted the Lebanese army to fire back and “respond to the sources of fire”, Lebanon's presidency said on Monday in a statement on X. It added that the clashes "cannot go on, and we will not accept its continuation". The Lebanese army said it has responded using “appropriate weapons” to the shelling of Lebanese villages and towns, coming from Syria.
Hussein Al Hajj Hassan, a member of Hezbollah and a Lebanese MP, said the group “has no relation to what happened on the border”.
The Iran-backed Hezbollah is the only non-state group allowed to carry arms in Lebanon, a legacy of previous support from Syria's former Assad regime, when it was the dominant power in Lebanon after the end of the civil war in 1990.
Hezbollah and other Shiite militias provided support for Mr Al Assad, which enabled him to crush a 2011 uprising against his rule and survive the ensuing civil war until he was deposed last year. An offensive by the Assad regime in 2020, with backing from Hezbollah and Russia, attempted to dislodge HTS from its rebel base in northern Syria but failed. Mr Al Assad's eventual toppling in December during an 11-day advance led by HTS prompted the withdrawal of Iran and its allies from Syria.
The fall of the Assad regime ended Syria's sway over Lebanese affairs, a hallmark of ties between the two countries since the late Syrian president Hafez Al Assad sent troops into Lebanon shortly after the outbreak of the 1975-1990 civil war. Lebanese Foreign Minister Youssef Rajji said this month that discussions have begun with Damascus on scrapping a joint council viewed as a control mechanism over Lebanon and on demarcating the shared border.

HTS and Hezbollah have clashed several times at the border since Mr Al Assad's downfall, with the authorities in Damascus saying some smuggling rings Hezbollah used to supply weapons from Iran still operate in the area.
However, the killing of the three four and the manner in which their lives ended have fuelled a more forceful reaction this time.
A Lebanese official said the roots of the escalation were unclear. Either fighters from the Syrian side crossed into Lebanon and were killed by local tribes, or Hezbollah fighters may have entered Syria, he said.
According to the official, who spoke on condition of anonymity, Lebanese groups linked to HTS have the capacity to launch attacks on Hezbollah inside Lebanese territory and further escalate the situation.
Another Lebanese political source blamed HTS for the escalation, calling it a border infiltration by HTS that aims to put pressure on Hezbollah and aligns with US and Israeli goals for the disarmament of the group. "Syrian allegations that Lebanese [forces] had entered the Syrian side are completely untrue," the source said.
The Saudi-owned Al Arabiya Television said two of its reporting crew had been injured by a Hezbollah rocket while covering the clashes.
HTS has been also engaged in a campaign to spread government control over coastal areas near the border with Lebanon that constitute a reservoir of support for the Assad regime, particularly among the Alawite minority to which Mr Al Assad belongs.
At least 1,400 Alawites, the vast majority civilians, have been killed in the campaign over the past two weeks, prompting 10,000 members of the sect to cross into Lebanon, looking for safety.
They have settled in northern towns and areas. Lebanon now fears that sectarian violence from Syria’s coast could spill over into its volatile north in the adjacent Bab Al Tebbaneh and Jabal Mohsen districts of Tripoli, where Sunni and Alawite gunmen have engaged in deadly clashes several times in the past 15 years.