The attack near the eastern border town of Arsal came after forces loyal to Syrian President Bashar Al-Assad routed rebels from two Syrian villages lying just across the border.
The bombing demonstrated how far the war in neighboring Syria has sucked in its fragile neighbor, igniting violent sectarian tensions between Sunni extremists in Lebanon against the country’s Shi’ites, and ensnaring even the military.
Sunni extremists have accused Lebanon’s military of being partial to their rivals, the Shi’ite group Hezbollah, whose fighters are waging war in Syria alongside Assad’s forces.
The bomb killed three soldiers and wounded another four, a military statement said. Military helicopters rushed to rescue the wounded from the rugged mountainous area, said the army statement.
The Ahrar Al-Sunna in Baalbek Brigade, an extremist Sunni group, claimed responsibility for the bombing.
The group described the attack as a “heroic operation that targeted the crusader army in Arsal” in a message posted on Twitter.
The group said the bombing was to avenge the Lebanese army killing of a suspected militant during an arrest raid on Thursday, and for Hezbollah’s participation in the Syrian conflict.
The Shi’ite group “should not think it will not be punished for killing innocents in Syria,” one message read. “As long as Sunnis in Lebanon are targeted, be assured we will respond,” said another.
The bombing shook windows in the town of Arsal, less than a mile (one kilometer) away, said deputy mayor Ahmad Fliti.
“People rushed outside to see what was happening, but the military closed off the area,” he said.
Following the bombing, a woman and child were killed by Lebanese soldiers who opened fire on their vehicle after the drive did not stop at another Arsal checkpoint, Lebanon’s state news said.
The bombing came after assailants killed two Lebanese soldiers in the northern town of Tripoli last week, and tried to kill a third.
There have been raging clashes between two Tripoli neighborhoods, in fighting linked to the Syrian war.
At least 11 Lebanese soldiers have been killed in similar attacks since December, including Saturday’s incident, according to an Associated Press count.
Attacks against the army are seen as shocking in Lebanon, where the military is viewed as the sole institution that represents, and unifies, the country’s squabbling sects. Despite hard-line Sunni anger against the army, Sunnis make up at least one-third of all military personnel.
Dozens more Lebanese civilians have been killed in bombings that have targeted mostly Shi’ite areas since last summer, also in retaliation for Hezbollah fighting in Syria.
The Iranian-backed Shi’ite group began waging war alongside Assad’s forces last year, allowing Syrian forces to regain swaths of territory lost to armed rebels since the uprising began three years ago.
Hours before the bombing, Hezbollah leader Sheik Hassan Nasrallah said his fighters would remain in Syria for now.
Speaking at a cultural event in south Lebanon, the black-turbaned cleric said Hezbollah fighters in Lebanon were defending Syria and their own country from the scourge of extremist Sunni groups.
“We have taken on this burden and are continuing with it,” Nasrallah said in a speech broadcast from a secret location.
On Saturday, they captured two villages near the border with Lebanon on Saturday, continuing a weeks-long advance that has cut a major supply route for weapons and fighters into the country from eastern Lebanon, said activists and state TV.
The villages of Flita and Ras Maara were the latest targets of a government offensive in the rugged Qalamoun border region after troops captured the town of Yabroud earlier this month.
Flita lies about 5 miles (7 kilometers) from the border town of Arsal.
The Britain-based Syrian Observatory for Human Rights also confirmed Syrian forces backed by fighters of the Shi’ite Lebanese group Hezbollah seized the villages.
Earlier, Lebanon’s state-run National News Agency said about 700 Syrians had fled the fighting to nearby Arsal.
Lebanese soldiers were checking people’s identity cards to make sure no fighters were among them, it said.
An activist in a nearby area who uses the name of Abu Yazan Al-Shami said rebels expected Assad-loyal forces to try to seize the town of Rankous next, allowing the government “to completely cut supplies from Lebanon into Qalamoun.”
The Syrian Observatory said by Saturday evening, government forces were attacking the outskirts of Rankous.