BEIRUT — Thousands of Syrians poured into Lebanon over the past two days, taking shelter in wedding halls and makeshift shacks after fleeing heavy fighting in a rugged mountain region across the border in western Syria, UN and local officials said Sunday.
The clashes in Qalamoun, an area that stretches from north of the Syrian capital along the Lebanese frontier, appeared to be part of a long-anticipated government offensive aimed at cutting a key rebel supply route and cementing President Bashar Assad’s hold on the strategic corridor from the capital to the coast.
Over the past month, Assad’s forces have made headway against the rebels on two key fronts, capturing a string of opposition-held suburbs south of Damascus and taking two towns and a military base outside the northern city of Aleppo.
A government victory in the battle for Qalamoun would deal a severe blow to the already beleaguered rebels on the doorsteps of Damascus.
Despite the recent setbacks on the capital’s southern periphery, the opposition remains firmly entrenched in other areas around Damascus and capable of carrying out large attacks.
A massive explosion late Sunday targeting an administrative office in the northeastern suburb of Harasta killed at least 31 government troops, the Britain-based Syrian Observatory for Human Rights said. There was no immediate confirmation from government officials or state media.
Since the heavy fighting in Qalamoun began Friday, some 10,000 Syrians have fled across the border to the Lebanese frontier town of Arsal, former mayor Bassel Hojeiri said. The new arrivals have crammed into wedding halls and improvised shacks, Hojeiri said.
Some families left so quickly that they arrived in Lebanon ‘‘without anything except the clothes on their backs,’’ said Dana Sleiman, who works for the United Nations High Commissioner for Refugees.
She said at least 1,000 Syrian families crossed into Lebanon over the weekend, but many had not yet registered with the United Nations, so more precise figures weren’t available.
Sleiman said some of the new arrivals settled into tin shack slums that dot eastern Lebanon’s Bekaa Valley, and they were being offered thick plastic to reinforce their shelters against the cold.
The UN refugee agency was also distributing blankets, mattresses, food, diapers, and hygiene kits to the refugees.
The new refugees join an estimated 1.4 million Syrians — 800,000 of whom have registered — who have already found shelter in Lebanon, according to Lebanese officials.
The massive influx has proven a burden for Lebanon and has helped stoke the country’s already simmering sectarian tensions.