Rebels seeking to topple Syrian President Bashar Assad are trying to carve a pathway from the Jordanian border through the southern province of Daraa, in what is seen as their best shot at capturing Damascus.
A few weeks ago, they scored significant gains, but have since suffered setbacks in a regime counteroffensive.
In recent days, regime troops and rebel fighters battled over Khirbet Ghazaleh, a town near the Damascus-Jordan highway.
Regime forces retook Khirbet Ghazaleh on Sunday and rebels withdrew from the area, said Rami Abdul-Rahman, head of the Britain-based Syrian Observatory for Human Rights.
Troops reopened the highway, restoring the supply line between Damascus and the contested provincial capital of Daraa, he said. Regime forces were carrying out raids and searching homes in Khirbet Ghazaleh on Monday.
Damascus, still overwhelmingly under regime control, is the ultimate prize in a largely deadlocked civil war.
Rebels control large parts of the countryside in northern Syria, but those areas are further away from the capital than the Jordanian border.
Arab officials and Western military experts have said Mideast powers opposed to Assad have stepped up weapons supplies to Syrian rebels, with Jordan opening up as a new route.
The uprising against Assad erupted in March 2011 and escalated into a civil war. Over the weekend, the Observatory issued a new death toll, estimating that more than 80,000 Syrians have been killed, almost half civilians. In February, the U.N. said at least 70,000 Syrians were killed.
Western leaders are facing growing pressure to find a way to end the conflict — both because of the rising death toll and fears that neighbouring Israel or Turkey could inadvertently get pulled deeper into it.
Turkey has blamed the Assad regime for twin car bombs Saturday that killed 46 people and wounded scores in a Turkish border town that serves as a hub for Syrian refugees and rebels.
Turkey signalled restraint Sunday, saying it won't be dragged into the quagmire, but tensions between the former rivals are running high.
Earlier this month, Israel attacked suspected shipments of advanced Iranian missiles in Syria with back-to-back airstrikes. Israeli officials signalled there would be more such attacks unless Syria refrains from trying to deliver such "game-changing" missiles to ally Hezbollah, an anti-Israel militia in Lebanon.
For now, the West is placing its hopes on a diplomatic plan that ran aground in the past but now appears to have stronger Russian backing.
Last week, the U.S. and Russia agreed to revive the idea of negotiations between Syria's political opposition and members of the regime on a transitional government, accompanied by an open-ended cease-fire.
Through the conflict, Russia sided with Assad, sending him weapons and shielding him against Western attempts to impose international sanctions.
However, British Prime Minister David Cameron suggested en route to a White House meeting with President Barack Obama that Russia is ready to find common ground with the West. Cameron met last week with Russian President Vladimir Putin to discuss the new Syria initiative.
"While it is no secret that Britain and Russia have taken a different approach to Syria I was very struck in my conversations with President Putin that there is a recognition that it would be in all our interests to secure a safe and secure Syria with a democratic and pluralist future, and end the regional instability," Cameron said late Sunday. "We have got a long way to go, but they were good talks."