The Lebanese army will not coordinate with the Syrian army to fight against ISIS in the Lebanese-Syrian border zone, a military source told Reuters on Saturday, rejecting a local media report of direct military cooperation between the two.
The source said the Lebanese army had the military capability to confront and defeat the group without any regional or international support.
The presence of ISIS and Nusra Front militants in pockets on Lebanon's border is the biggest military spillover into the country from Syria's civil war.
An offensive launched last month by Lebanon's Hezbollah - a key ally of Syrian President Bashar al-Assad - forced Nusra Front militants to leave for a rebel-held area in northwest Syria under an evacuation deal.
The Lebanese army did not take part in that offensive, but has been widely expected to lead an attack against the ISIS pocket.
On Friday Hezbollah leader Sayyed Hassan Nasrallah said an assault on ISIS militants in the border zone would begin in a few days.
He said the Lebanese army would attack ISIS from the Lebanese side of the border while Hezbollah and the Syrian army would simultaneously attack from the Syrian side.
Hezbollah has been fighting alongside the Syrian army against rebels including hardline Sunni Islamists in Syria.
On Saturday Lebanese newspaper al-Joumhouria reported from sources that direct military coordination had occurred between the Syrian and Lebanese armies regarding the upcoming offensive against ISIS.
The military source said the Lebanese army had been attacking ISIS for some time, by preventing it spreading further and cutting supply routes.
Lebanese state news agency NNA and a Hezbollah media unit said on Saturday the Lebanese army had shelled ISIS positions in the Ras Baalbek and al-Qaa areas of northeast Lebanon.