Mohammad Darra Jamo, a commentator who worked for Syrian state media, killed by gunmen in southern town of Sarafand
Militants have assassinated a well-known supporter of the Syrian president, Bashar al-Assad, in Lebanon, security sources say, the latest sign of Syria's civil war spreading to its smaller neighbour.
Mohammad Darra Jamo, a commentator who worked for Syrian state media and often appeared on Arab TV channels, was attacked by gunmen hiding in his house in the southern town of Sarafand, the sources said.
His wife was with him but was unharmed, they added.
The Syrian state news agency Sana blamed an "armed terrorist group" for the killing, which took place at around 2am on Wednesday local time. Lebanese security sources said supporters of the Syrian rebel opposition were the leading suspects.
Lebanon, whose own 15-year civil war ended in 1990, is struggling to stay on the sidelines of Syria's conflict. Car bombs and clashes between groups supporting opposite sides of Syria's war have become increasingly common.
On Tuesday, a convoy carrying members of the Lebanese Shia militant group Hezbollah was hit by a roadside bomb and ambushed near the Syrian border, killing one official and wounding two others.
Syrian Sunni rebels have threatened to strike Hezbollah, one of Lebanon's most powerful political and military forces, in Lebanon following its military support of Assad in Syria.
Last week, a car bomb injured more than 50 people in a southern Beirut suburb controlled by Hezbollah. In late May, rockets were fired at a Hezbollah area of southern Beirut.
Syria's civil war started with pro-democracy protests that were suppressed by government forces. The ensuing civil war has killed 90,000 and drawn in regional powers hoping to sway the outcome of the conflict.
On Tuesday, the United Nations warned that an estimated 5,000 Syrians were dying every month and refugees were fleeing at a rate not seen since the 1994 Rwanda genocide.
"In Syria today, serious human rights violations, war crimes and crimes against humanity are the rule," Ivan Simonovic, the assistant secretary general for human rights, told the UN security council.
He added that "the extremely high rate of killings … demonstrates the drastic deterioration of this conflict".
The UN refugee chief Antonio Guterres said two-thirds of the nearly 1.8 million Syrian refugees known to the agency had fled since the beginning of 2013, an average of more than 6,000 a day.
"We have not seen a refugee outflow escalate at such a frightening rate since the Rwandan genocide almost 20 years ago," he said.
The UN humanitarian chief Valerie Amos said at least 6.8 million Syrians required urgent humanitarian assistance and accused the government and opposition of "systematically and in many cases deliberately" failing in their obligation to protect civilians.
"This is a regional crisis, not a crisis in Syria, with regional consequences, requiring sustained and comprehensive engagement from the international community," Amos said by video conference from Geneva.
"The security, economic, political, social, development and humanitarian consequences of this crisis are extremely grave and its human impact immeasurable in terms of the long-term trauma and emotional impact on this and future generations of Syrians," she said. "We are not only watching the destruction of a country but also of its people."