A Syrian helicopter has flown 20km into Lebanon and fired on an area on the outskirts of a Lebanese town, officials and residents say.
"Two rockets were launched, though no casualties were caused," Ahmad Fliti, deputy mayor of Arsal, told AFP news agency on Wednesday. "There are several houses in the area where the rockets landed."
Another official, speaking on condition of anonymity told AFP that a helicopter fired two rockets on Jubaneh al-Shmis on the outskirts of Arsal.
"The area lies several hundred metres away from a Lebanese army checkpoint," he said.
Arsal is a majority Sunni town in northeastern Lebanon, many of whose residents support the revolt against President Bashar al-Assad in neighbouring Syria.
Residents of Arsal told Al Jazeera that two or three missiles hit the area, and houses have been affected.
This is the first time a Syrian air raid has hit the town of Arsal.
The area lies on the border with Syria, and has become home to thousands of people fleeing their the conflict. Arsal hosts more than 20,000 Syrian refugees, which is almost half the half the population of Arsal.
Scores of Syrians injured in the violence have been brought into Arsal for medical treatment in recent months, and there have been reports of fighters and arms being smuggled in.
The attack comes after reported air strikes in the same area last month, which were condemned by the US and by Lebanese President Michel Sleiman who called it an "unacceptable violation".
Damascus denied responsibility for the attacks.
Syria's conflict, which has raged for more than two years, has further entrenching deep divisions in Lebanon.
Lebanon's Sunni-led March 14 movement supports the opposition fighters, but the powerful Shia movement Hezbollah and its allies back the Assad regime.
In other developments in Lebanon on Wednesday, the first shipment Russian humanitarian aid for Syrian refugees landed in Beirut.
The Russian plane containing 36 tonnes of humanitarian aid contained blankets, food supplies and generators, Alexander Zasypkin, Russia's ambassador to Beirut, said.
The UN says 398,000 Syrians are seeking refuge from the conflict in Lebanon.
Russia has supported Assad throughout the revolt by refusing to consider sanctions on Syria, vetoing three resolutions condemning his crackdown on opposition groups and supplying weapons to the Syrian army.
Zasypkin said at the airport that Moscow would send another shipment of aid next week and two more later this month.