A Lebanese mediator was killed on Saturday in the second day of fighting between the powerful Hezbollah group and fighters near the border with Syria, the official news agency ANI said.

"Ahmad al-Fliti, who was mediating between fighters and Hezbollah ... was wounded when his car was hit by shelling of unknown origin in Juruod Arsal," ANI said.

"He later succumbed to his wounds."

Lebanon's army said Fliti, who was the former deputy mayor of Arsal, was killed in shelling by "the terrorist organisation of the Jabhat Fateh al-Sham", formerly known as the al-Nusra Front.

An escort of his was also injured in the attack, the army added.

Hezbollah on Friday said its fighters had begun an operation against fighters on both sides of the country's border with Syria.

On Saturday, Hezbollah announced several advances in the mountainous border area of Juruod Arsal.

Funerals were held on Saturday for 11 Hezbollah fighters killed in the clashes, nine in Beirut and two in Baalbek.

Lebanon's army has not officially announced its participation in the offensive, but said on Friday it had targeted "terrorists" in the area.

According to the UN refugee agency UNHCR, an estimated 45,000 Syrian refugees live in informal camps in Juroud Arsal after having fled the six-year war in their home country.

But security in the area has also long been a concern, with Lebanese forces battling rebels in the area in 2014.

Hezbollah on Friday also announced fighting on the other side of the border in Syria's Qalamoun, where the Lebanese Shia group has fought for years alongside President Bashar al-Assad's army against rebels.

Syria's air force on Saturday carried out air raids near the border, the Britain-based Syrian Observatory for Human Rights monitor said.

More than a million refugees have flooded into Lebanon since the Syria conflict erupted with anti-government protests in March 2011.

Their presence has been largely tolerated despite testing the limited resources and ageing infrastructure of a country of just four million.