Weeks of clashes between Syrian forces and opposition rebels along the border with Jordan escalated into a full-out war on Saturday, said Jordanian security sources, DPA reported.
The two sides battled fiercely for control of the border, with heavy shelling and rocket fire a few metres from the Jordanian territory, added the sources.
During the fighting, the rebel Free Syrian Army briefly gained control of the border Naseib crossing - near the southern Syrian city of the same name and across the Jordanian border city of Mafarq - before being repelled by forces loyal to President Bashar al-Assad.
"At one point, the Syrian rebel flag was flying over the crossing point," said a Jordanian security source on condition of anonymity because he was not authorized to speak to the media.
Despite being pushed back, the rebels' drive to control the Syrian-Jordanian border area is far from over, with the two sides locked in a "back-and-forth" volley of gunfire and artillery, added the source.
The push to control the Syrian-Jordanian border comes two days after Syrian rebels announced they had seized crossing posts along Syria's borders with Turkey and Iraq.
Activists say Saturday's clashes marked only "the beginning" of a wider campaign to secure Syria's border areas and ensure the safe passage of Syrian civilians and deserters from the homeland.
"It has always been the Free Syrian Army's priority and responsibility to ensure that the people are able to find places of safety and receive medical treatment," said Abu Ahmed, a member of the Syrian opposition grouping, the Local Coordination Committees.
"Controlling the borders with Jordan and Turkey is a key to fulfilling this responsibility," added Abu Ahmed, currently residing in Jordan.
The latest clashes come as a bid by rebels to break a months-long military blockade, which has prevented Syrian civilians from entering Jordan.
Opposition activists say al-Assad's forces have openly targeted refugees attempting to flee violence in Syria.
The escalation in fighting also comes amid shelling attacks near the border region, which residents claim are creeping closer to Jordan.
"At the start of the crisis, we would hear an explosion one day, gunfire the next," said Hassan Zoubi, a resident of the border city of Ramtha, a few kilometers away from the Syrian province of Daraa.
"Now we can no longer sleep at night. It is as if the war has arrived to Jordan," he added.
The Syrian rebels' push to control the country's border regions comes two days after a daring bomb attack inside Damascus that killed four core members of al-Assad's inner circle, including his brother-in-law, Assef Shawkat.
Following the Damascus attack, the Jordanian army dispatched an additional 10,000 soldiers to the northern border region.
The move marked only the second time Jordan decided to boost security forces in the area.
As the Syrian conflict reaches a tipping point, observers say Jordan is struggling to maintain its long-held stance of neutrality, largely driven by fears that the crisis could spill over across its border.