The Nusra Front, al-Qaeda's affiliate in Syria, has killed one of the Lebanese soldiers it had been holding in captivity, according to Lebanese security sources and a Twitter statement.
The killing of the soldier, if confirmed, will be the first to have been carried out by the Nusra Front, which along with ISIL is holding over a dozen more Lebanese soldiers captive.
The Twitter statement on an account affiliated with Nusra Front said on Friday that the soldier had become "the first victim of the intransigence of the Lebanese army which has become a plaything in the hands of the Iranian party", referring to Hezbollah.
Live Box 2012108933861442
However, the father of the soldier said on local Lebanese TV and radio that the news of his son's death was only a rumour. "I have not spoken with the abductors, only with the mediators. The news of his death till now is untrue," he said.
Sunni opposition fighters and other rebels in Syria regularly accuse the Lebanese army of working with Hezbollah, the Lebanese Shia armed group which has sent fighters to help the forces of Syrian President Bashar al-Assad.
Two Lebanese soldiers were also killed by a roadside bomb on Friday near the border town of Arsal, security sources said, the first such attack since the fighters from Syria staged an incursion there last month in the worst spillover to date of the Syrian civil war into Lebanon.
The fighters, including armed men affiliated with the Islamic State in Iraq and the Levant (ISIL) group, seized a number of Lebanese soldiers during that incursion.
ISIL fighters have beheaded two of those soldiers since then.
Sunni fighters have been demanding the release of Nusra and ISIL members held in a Lebanese jail.
Three soldiers were wounded in Friday's bomb attack, which targeted a military personnel carrier.
Following the bombing, soldiers raided houses in the town in search of fighters, security sources said, and later, according to the state news agency, the army used "heavy weapons" to target their positions around Arsal near the border with Syria.
The Sunni Muslim town has become a refuge for tens of thousands of Syrians fleeing the country's civil war.
Two rockets fell in the area of the town of al-Labwe near Arsal but no casualties were reported, security sources said.
Earlier on Friday, Lebanese soldiers arrested two Syrians in the Bekaa Valley town of Baalbek who had confessed to belonging to the Nusra Front, security sources said.
Security forces also detained six Syrians in the predominantly Shia town of Nabatiyeh in southern Lebanon who had confessed to membership of "terrorist groups", a security official said.
One had been found in possession of explosive belts, he said.