Lebanon put its army on alert Saturday after three people were killed in a cross-border shelling from the Syrian territory, raising concerns that the 16-month conflict in Syria might spill over into neighbouring countries, DPA reported.
"Army units in the (border) area of Wadi Khaled are on high alert and the required field measures are in place to tackle any violation along the Syrian-Lebanese border," the army said in a statement.
The steps were taken after three women were killed and seven others wounded as some 20 shells fell on the town of Al-Heesah in Wadi Khaled, 185 kilometers north of the capital Beirut.
It was the deadliest incident on the Lebanon-Syria border since the popular uprising started in Syria in March 2011.
Syrian troops have carried out several cross-border incursions into northern Lebanon, where some 22,000 Syrians have sought refuge from the violence in their homeland.
Lebanese President Michel Suleiman voiced regret about the latest incident and said "the safety of the Lebanese citizens is our top priority," according to the Lebanese National news Agency.
"This is a flagrant violation of the Lebanese sovereignty. I call on the president to take immediate action to protect the innocent Lebanese living in the area," lawmaker Ahmad Fafat, who is from northern Lebanon, told dpa by phone.
The shelling, allegedly by forces loyal to Syrian President Bashar al-Assad, prompted residents to flee to safer areas, reported local witnesses.
"Our house was hit by at least two shells. I managed to save my children from being killed," Abu Ahmed al-Owaichi, whose sister was among the three victims, told dpa.
"Shortly before the shelling started at dawn, we heard sounds of heavy machine guns rattling in the neighbouring Syrian area of al-Kussair," he added.
According to Syrian state television, security forces had foiled an attempt by "terrorist groups" coming from Lebanon to infiltrate al-Kussair in the central province of Homs.
The broadcaster added that government forces had killed "dozens of terrorists."
Elsewhere in Syria, at least 33 people were killed by al-Assad's forces, mainly in the restive northern province Idlib and in the town of Deir al-Zour, in the east.
Activists in Idlib said at least 20 soldiers had defected and joined the opposition rebels in the nearby area of Maaret al- Noumaan, where heavy clashes raged between government forces and rebels on Friday.
Defections from the Syrian army have recently been on the rise, according to the opposition.
The most prominent instance was the desertion of Brigadier General Manaf Tlass, a friend of al-Assad. He fled this week to Turkey before heading to France.
The surge in violence comes as the Syrian opposition has been calling on the United Nations to beef up its monitoring mission in the country.
"The number of observers should be increased, not decreased. They should be armed to protect themselves and become a deterrent force at this critical time of the Syrian crisis," Burhan Ghalioun, the former head of the opposition Syrian National Council, told dpa from Paris.
Ghalioun was commenting on a report by UN chief Ban Ki-moon to the UN Security Council, in which he called for scaling back the unarmed observer mission in Syria.
Ban also recommended that the mission, with a "reduced military observer component," be redeployed to the capital Damascus.
He added that the smaller mission should instead focus on promoting political dialogue rather than monitoring a shaky ceasefire.
The Security Council must make a decision on the mandate and future of the 300-strong team by July 20.
A UN source in Beirut told dpa that several countries with observers in Syria were threatening to withdraw due to the spike in violence in the Middle Eastern nation.
Last month, the mission's chief suspended its activities, citing what he called "unprecedented" levels of violence.