BEIRUT -- Syrian rebels killed 10 Lebanese troops and likely captured over a dozen more in a raid on a Lebanese border town, the country's military chief said, the most serious spillover of violence yet into the tiny country from its neighbor's civil war.
The capture of Lebanese soldiers and police raised fears that the country could become further entangled in the Syrian civil war and could worsen already-brewing sectarian tensions.
"What happened today is more serious than what some people imagine," Lebanon's army chief, Gen. Jean Kahwaji, told journalists.
As fighting raged Sunday, some residents tried to flee from the eastern Lebanese border town of Arsal, home to 40,000 residents and 120,000 Syrian refugees.
The attack began Saturday as Syrian rebels made a cross-border raid into Arsal, some 90 kilometers (55 miles) from the capital, Beirut. The clashes continued into Sunday around the municipal building and an army checkpoint, Lebanon's state news agency reported. Local television footage showing wailing ambulances racing into town and soldiers standing guard just outside its limits.
The raid came hours after the army said troops detained Syrian Imad Ahmad Jomaa, who identified himself as a member of the Nusra Front. The state-run National News Agency said Jomaa was detained as he was being brought to a hospital in Lebanon after being wounded while fighting Syrian troops.
The Nusra Front is one of the most powerful groups fighting to overthrow the rule of Syrian President Bashar Assad.
The army chief said the fighters belonged to extremist Sunni groups, but did not name them. He said the fighting had killed 10 soldiers, while 13 were missing.
"They may be prisoners of terrorist groups," he said.
A video uploaded to an account associated with the Nusra Front showed over a dozen captured Lebanese soldiers and police officers. In the video, the men announced their defections from the Lebanese army and the Shiite militant group Hezbollah, whose forces are fighting in Syria in support of Assad.
The video of the men's capture appeared authentic and corresponded with Associated Press reporting on the attack in Arsal. But the men appeared uncomfortable as they repeated similar statements as many refused to look at the camera.
A trickle of vehicles packed with residents fled Arsal on Sunday. Thousands more were stuck, said Mohammed Ezeldeen, who drove to Beirut in a car packed with 15 people.
"Between the shelling and shelling, there's shelling," Ezeldeen said by phone. "People can't leave because there are clashes around the main checkpoint."
Deputy Mayor Ahmad Fliti said rebels killed three civilians when residents rushed to defend the town's police station. Arsal resident Ezeldeen said he heard a similar account.
The deputy mayor said another seven Syrian refugees were killed after a shell slammed into the tent encampment. United Nations officials, who oversee Syrian refugees in Lebanon, did not respond to requests for comment.
Syria's civil war has spilled over into Lebanon on multiple occasions, and inflamed sectarian tensions between Sunnis and Shiites, leaving scores dead. However, previous rebel raids never went so deeply into Lebanese territory. Rebels also directly challenged Lebanese security forces for the first time in their assault on Arsal.
Lebanon's Sunni and Shiite communities have lined up on opposing side of Syria's civil war. Sunnis, including those in Arsal, broadly support the Sunni rebels fighting against Assad. Tens of thousands of Syrian refugees live in and around Arsal and rebels sometimes use the town as a base. Shiites typically back Assad.
Syria's conflict began in March 2011 as a popular uprising against Assad's rule, but turned into an insurgency after government forces violently cracked down on demonstrators. It has since become civil war with sectarian overtones. Over 170,000 people, mostly combatants, have been killed in Syria in more than three years of fighting, activists say.
The killed included at least 34 people from government shelling of a market in the rebel-held town of Kafr Batna and the nearby town of Douma, both near the capital, Damascus on Sunday, said activists.
The Britain-based Syrian Observatory for Human Rights said the toll was likely to rise from the airstrikes. Activist Husam Taqieldeen, who also reported the strikes, provided a higher death toll. Conflicting death tolls are common after such attacks.
The Observatory obtains its information from a network of activists on the ground.
Also in the capital, mortar shells that crashed into residential areas killed 11 people, including women and children, and wounded at least 20 others, state-run news agency SANA said. Most of the deaths occurred in the Dweilaa district, the agency added.
Rebels in suburbs of the capital frequently fire mortars at Damascus, seat of Assad's power.