Fighting erupted along three of Syria’s fractious borders Friday, in an acute reminder of the potential for the country’s civil war to spark a regional conflagration.
Israel’s army fired artillery into Syria Friday night after gunshots and shells were directed at soldiers on the Israeli-occupied sector of the Golan Heights , the Israeli military said.
In Homs, Syrian forces battled rebels near the border with Lebanon as part of a counteroffensive aimed at regaining control of territory.
Meanwhile, fighting between rebels and opposition forces also broke out in the eastern city of Qamishli on the Turkish border, ending a de facto truce in the mainly Christian and Kurdish area.
With a fresh influx of arms, opposition fighters have made significant gains in the past weeks, particularly in the southern province of Deraa, where rebels have been advancing in the region between the Jordanian border and the capital, Damascus.
The province of Homs and its capital were the scenes of some of the heaviest fighting  during the first year of Syrian conflict. The violence has escalated there in recent weeks, with Syrian warplanes bombing the city daily.
In the past two days, troops have clashed with rebels on the edges of the province along the Lebanese border, in some of the worst fighting in the area in months.
Sporadic explosions inside Syria could be heard from the Lebanese side of the border Friday and an Associated Press reporter said Syrian warplanes carried out at least one airstrike inside Syrian territory.
The border area is strategically important to both sides fighting in Syria’s civil war and battles there have been frequent in past weeks, particularly in and around the town of Al-Qusair. The area is considered vital to the Syrian regime because of its location along a road linking Damascus with Homs – a strategic supply route for the military .
The opposition activist group the Syrian Observatory for Human Rights  said Friday’s clashes between soldiers and rebels were concentrated around Al-Qusair.
Overlooking Al-Qusair from the Lebanese side are villages populated mostly by Shiite Muslim supporters of Hezbollah, which has backed President Bashar Assad’s regime throughout the 2-year-old conflict.
In the Lebanese village of Al-Qasr, which is on the opposite side of the border from Al-Qusair, residents said they had gotten used to the shelling.
“Yesterday, the explosions were nonstop,” Ali Nasereddine said, sitting in the garden of his house, less than 100 meters from a Syrian army post.
Syrian warplanes carried out airstrikes around the country Friday, hitting targets in Deraa in the south, in Hassakeh province in the northeast near the border with Turkey and in the northern city of Aleppo, parts of which have been under rebel control since last summer.
The fighting in Qamishli marked the first serious outbreak of violence there since the beginning of the uprising. Qamishli has remained peaceful mainly because local Kurds agreed with mostly Arab rebels to avoid clashes within city limits, said the Observatory. The city of around 200,000 has become home to thousands of Syrians who have fled other parts of the country.
Videos posted online Friday showed trucks and dozens of rebels preparing an attack on Qamishli’s domestic airport and smoke rising from the airport grounds. Inhabitants are now waiting to see whether Assad’s forces retaliate for rebel attacks by using war planes.
The Observatory said the advance includes rebels of the Free Syrian Army and the hard-line Islamist Nusra Front , who have clashed in the past with Christians and Kurds whom the opposition has tried to persuade to abandon Assad.
“We are not sure why they are attacking today,” said Observatory chief Rami Abdel-Rahman. “Maybe the agreement broke down,” he said, adding that the government and Kurdish militia control different areas of Qamishli.
In January, Kurdish militants and rebels fought battles with each other for weeks after Assad’s forces retreated from Ras al-Ain.
The Israeli retaliatory fire was the latest uptick in stray fire on the Golan in recent months.
The Israeli army said no soldiers were injured and no damage was caused, but that Israeli army “soldiers responded with artillery fire toward the source of the shooting.”
The latest violence came a day after Assad’s regime called on the U.N. Security Council to class Al-Nusra Front as an Al-Qaeda-linked group, after its head pledged allegiance this week to Al-Qaeda leader Ayman al-Zawahri.
France said Friday the Security Council has begun informal talks on whether to impose sanctions on the rebel Nusra Front as a result of the pledge.
The militant Islamist element of the Syrian conflict poses a quandary for Western powers and their Arab allies, which are alarmed by Sunni Muslim jihadi fighters whose fiercely anti-Shiite ideology has fueled sectarian tensions in the Middle East.
“It is one solution that we are studying and discussing informally with our U.N. Security Council partners and European allies,” French Foreign Ministry spokesman Philippe Lalliot said.
The Nusra announcement has also infuriated other opposition elements who say it helps the regime. Assad has long justified his brutal assaults as a war against foreign-backed jihadists.
“One thing is for sure. When the request is officially made, France will refuse any attempt by the Syrian regime that tries through this to label all the Syrian opposition as terrorists,” Lalliot said.