Lebanese President Michel Suleiman has condemned a Syrian air strike on Lebanon's side of the border between the two countries, calling it an "unacceptable violation" of Lebanese sovereignty.
The president's comments on Tuesday were a rare rebuke of Syria, a powerful, larger neighbour that once dominated
Syrian air force jets fired four rockets at a remote section of the border with Lebanon on Monday, security sources said, four days after Damascus warned it may strike at Syrian rebels taking refuge across the frontier.
Many residents of the border town of Arsal back the uprising against Syrian President Bashar al-Assad.
Local residents said the missiles had fallen in an agricultural area and there were no injuries in the incident. There are an estimated 15,000 Syrians taking refuge in Arsal.
Al Jazeera's Rula Amin, reporting from Arsal, said the local residents were very concerned of the attack, fearing more strikes.
"It's a very serious development," our correspondent said. "Most Lebanese politicians were very alarmed by this airstrike."
But in a statement on state television, Syria's foreign ministry said the country "stresses its respect for Lebanese sovereignty and its support for Lebanon's security and stability".
Lebanon, which had its own civil war from 1975 to 1990, has maintained a policy of "dissociation" from Syria's two-year conflict.
Suleiman has criticised Damascus in the past when deadly clashes spilled across the border.
The US State Department has also condemned the strike as "a significant escalation" of violence.
"These kinds of violations of sovereignty are absolutely unacceptable," State Department spokeswoman Victoria Nuland told reporters at her daily briefing.
On Thursday, Syria's Foreign Ministry claimed that a "large number" of opposition fighters had crossed Lebanon's northern border into the Syrian town of Talkalakh last week.
"Syria expects the Lebanese side to prevent these armed terrorist groups from using the borders as a crossing point, because they target Syrian people and are violating Syrian sovereignty," it said in a message to the Lebanese government, according to state media.
It said Syria's "patience is not unlimited", even though "Syrian forces have so far exercised restraint from striking at armed gangs inside Lebanese territory."
Lebanon’s opposition largely backs the Syrian uprising, while Hezbollah and its allies stand by Assad's regime.
Syrian rebels accuse Hezbollah of dispatching fighters to battle alongside Assad's force.
The United Nation said the two-year conflict has already killed more than 70,000 Syrians.