The capture of Yabrud on Sunday by Syrian troops came shortly after the conflict entered its fourth year and marked a significant setback for the foreign backed militants as it severs their supply lines from across the border.

It also raised fears of further spillover of the conflict into Lebanon, where extremists carried out a suicide car bomb attack late Sunday in a southern area that killed two people.

A security source in Damascus said the army would soon launch operations "in all areas where terrorists are to be found."

"The aim of the army operation is to entirely secure the border and to close all corridors to Lebanon."

The fighting along the border has sparked a fresh flight of civilians into Lebanon, which is already hosting nearly a million refugees, according to the UN High Commissioner for Refugees.

"So far 150 families have crossed the border since Yabrud fell," said the UNHCR's Lisa Abu Khaled.

"NGOs there were on standby so they have handed out food, blankets, etc, and the UN plans to register the arrivals this week."

Speaking to AFP via the Internet from the Qalamoun mountains, activist Jawad al-Sayed said all civilians were "evacuated" from Yabrud before the town fell, either to areas nearby or to neighboring Lebanon.

The Lebanese military was also deployed in force on roads and border crossings in the country's east, in a bid to avert "the infiltration of car bombs and armed men," said the official National News Agency.

NJF/NJF