BEIRUT, Lebanon -- Syrian warplanes attacked targets inside eastern Lebanon on Monday, the official Lebanese National News Agency reported. It appeared to be the first time since the Syrian conflict began two years ago that the military had used its air force to strike at suspected rebel hideouts across the Lebanon border.
A brief dispatch by the news agency said that "warplanes affiliated with the Syrian Air Force" attacked the Wadi al-Khayl Valley area, near the Lebanese border town of Arsal, without specifying whether they had caused casualties or damage. The mountainous area is known for its porous border. It is considered a haven for Syrian insurgents, and the civilian population there largely opposes President Bashar al-Assad of Syria.
Al-Manar, the television broadcaster controlled by the Lebanese Shiite group Hezbollah, which supports Mr. Assad, said the warplanes had targeted two barns used by anti-Assad fighters. Agence France-Presse, quoting an unidentified Lebanese security services official, said at least four missiles were fired.
Syrian forces have occasionally fired guns or mortar rounds across the Lebanon border in clashes with anti-Assad fighters, but had never before used warplanes to attack suspected rebel positions inside Lebanese territory.
There was no immediate confirmation of the attack from the Syrian government. But it warned on Thursday that its forces might fire into Lebanon because of what it called repeated incursions by terrorist gangs, the standard official Syrian terminology for the armed opposition to Mr. Assad.
That warning, contained in a diplomatic protest delivered through the Syrian Embassy in Beirut, complained that "armed terrorist gangs have infiltrated Syrian territory in large numbers from Lebanon."
Lebanon's government, mindful of the long history of entanglements with its neighbor, has sought to remain neutral over the conflict in Syria. But sectarian tensions have been stoked by the conflict nonetheless, aggravated in part by the influx of more than 300,000 Syrians seeking refuge in Lebanon. Many of them are Sunnis, the Islamic sect that also forms the backbone of the insurgency. Mr. Assad's minority Alawite sect is an offshoot of Shiite Islam.
The warplane attack was at least the third serious border episode in the past few weeks, underscoring how the Syrian conflict has threatened to destabilize the Middle East. On March 4, anti-Assad insurgents in western Iraq killed dozens of Syrian soldiers who had temporarily sought safety on the Iraqi side of the border. On March 6, insurgents seized a group of United Nations soldiers on patrol in the disputed Golan Heights region between Syria and Israel, the first time international peacekeepers had been ensnared in the Syrian conflict, but they were released three days later.
News of the warplane attack coincided with unconfirmed reports of mortar fire in relatively affluent parts of Damascus. The Syrian Observatory for Human Rights, an opposition group based in Britain with a network of contacts inside Syria, reported that two mortar rounds had struck the bridge linking the Mezzeh neighborhood to Mount Qasyoun in Damascus, and that another mortar round had fallen in Mezzeh near the Ministry of Higher Education. It was unclear which side had fired them.
Hania Mourtada reported from Beirut, and Rick Gladstone from New York. Hala Droubi contributed reporting from Dubai, United Arab Emirates.
This article originally appeared in The New York Times.