BEIRUT - A mine blast killed three Lebanese soldiers Sunday as they were heading to take part in an offensive against the Islamic State group along the border with Syria, the army said.
Lebanon's army began its operation in the Jurud Ras Baalbek and Jurud al-Qaa region early on Saturday, and has already recaptured two thirds of the territory in the area, the military said.
The retaken area covers about 80 square kilometres (around 31 square miles) once controlled by the jihadists, the army said.
But an army source warned on Sunday that ousting IS from the rest of the territory would be tough.
"The toughest battle will be to retake the remaining 40 percent because it is there that Daesh fighters are gathered. Nevertheless the army is ready," said the source, using an Arabic acronym for IS.
The soldiers killed on Sunday were on their way to join the offensive to oust IS, the military said in a statement.
"An army vehicle was hit by a landmine on the Al-Najsa road roundabout in Jurud Arsal at noon today, killing three soldiers and injuring one soldier seriously," it read.
The statement said the wounded soldier was evacuated to hospital.
The battle against IS is being fought further north from Jurud Arsal, along the border with Syria.
The army also said soldiers blew up an explosives-packed car and a booby-trapped motorcycle carrying would-be suicide bombers in Jurud Ras Baalbek, preventing an attack on the troops.
Lebanon's battle against IS comes as the jihadist group faces assaults in both neighbouring Syria and Iraq, where the government early Sunday announced an offensive on the group's bastion of Tal Afar.
- Simultaneous Hezbollah offensive -
On Sunday, Lebanon's National News Agency reported soldiers used heavy artillery and rockets against IS positions in Jurud Ras Baalbek.
At least 20 IS fighters have been killed in clashes since the army unleashed its operation on Saturday, and 10 soldiers wounded, military spokesman Brigadier General Nazih Jreij said.
He said on the first day of the offensive that the army had captured around 30 square kilometres of territory.
The army says around 600 IS fighters were deployed in the Jurud Ras Baalbek and Jurud al-Qaa areas and controlled around 120 square kilometres of territory before the latest advances.
The offensive comes after Lebanon's powerful Shiite militant group Hezbollah waged a six-day assault against IS and Al-Qaeda's former affiliate in the Jurud Arsal area.
The operation ended with a ceasefire that saw around 8,000 refugees and jihadists transported to a jihadist-held area of northwestern Syria in return for the release of five captured Hezbollah fighters.
On Saturday, Hezbollah said it launched an operation against IS from the Syrian side of the border, where its fighters are battling alongside President Bashar al-Assad's army against rebels.
The Lebanese army denied any coordination with Hezbollah or the Syrian army.
Hezbollah's War Media outlet said its fighters and Syrian troops had "managed to liberate 87 square kilometres of the total area controlled by the Daesh organisation... in western Qalamun region" of Syria on Saturday alone.
On Sunday, the SITE Intelligence Group reported an IS claim that the jihadists had killed "nearly 100 Lebanese soldiers and Hezbollah fighters amidst clashes in western Qalamun".
Security along Lebanon's eastern border with Syria has long been a concern, and in 2014 jihadists invaded the town of Arsal and kidnapped 30 Lebanese soldiers and policemen.
Four were executed by their captors while a fifth died of his wounds.
Sixteen were released in a prisoner swap in December 2015, but another nine solders are believed to remain in IS hands, their fate unknown.
The army offensive against IS also comes after the jihadist group claimed several international attacks, including twin car ramming incidents in Spain that killed 14 people.
Lebanese soldiers raised the Spanish flag on a hilltop captured from IS on Saturday in a tribute to the victims of those attacks, the army said.