Syrian troops crossed into Lebanon on Tuesday, destroying farm buildings and clashing with Syrian rebels who had taken refuge there, residents and local security sources said.
They said Syrian forces crossed a few hundred metres into Lebanese territory. A security source in Beirut said clashes had taken place near the poorly marked border but did not confirm Syrian troops had entered Lebanon.
Shells hit north Lebanon last week and residents say Syrian troops have briefly crossed the frontier while pursuing fleeing rebels in recent months.
"More than 35 Syrian soldiers came across the border and started to destroy houses," said Abu Ahmed, 63, a resident of the mainly Sunni Muslim rural mountain area of al-Qaa.
Another resident said that the soldiers, some travelling in armoured personnel vehicles, fired rocket-propelled grenades and exchanged heavy machinegun fire with rebels. He said soldiers destroyed one house with a bulldozer.
The Lebanese army blocked off the area, where hundreds of Syrian refugees -- some of them active members of the rebel Free Syrian Army -- have fled a year-long revolt by mostly Sunni Muslim dissidents against President Bashar al-Assad, a member of Syria's Alawite minority, an offshoot of Shi'ite Islam.
Residents said the Syrian troops remained 200-500 metres inside Lebanese territory.
Lebanon has had a complicated relationship with Syria, which continues to exercise some influence over its neighbour despite the 2005 departure of thousands of Syrian troops and intelligence operatives from Lebanese soil.
Syria said on Monday that armed "terrorist groups" in Syria have been receiving weapons from supporters in Lebanon.
"Experts, officials and observers are unanimous that weapons are being smuggled into Syrian territory from bordering States, including Lebanon," Syria's U.N. Ambassador Bashar Ja'afari said in a letter sent last week to the U.N. Security Council and Secretary-General Ban Ki-moon.
Assad's forces have killed well over 8,000 people through the uprising, according to the United Nations. The Syrian government says "armed groups" have killed 3,000 members of the security services.