Separately, some 7,000 civilians were expected to be evacuated from two pro-government villages in northwestern Syria as part of a negotiated deal with insurgents who have besieged them for three years.
On the eve of the Trump-Putin summit in Helsinki, Damascus accused Israel of carrying out a rare strike far in the country's north near Aleppo, which was said to target "positions held by Syria's regime and its allies at the Neirab airport and around it", according to the Britain-based Syrian Observatory for Human Rights war monitor.
The rebel-linked Daraa Martyrs Documentation Office said 26 people were killed Wednesday in the Daraa countryside.
Khaled Solh, head of the local Syrian civil defense known as White Helmets, said only one ambulance was able to access the town and civilians relied on their cars to bring out at least 150 injured. The United States, which once armed the southern rebels, told them not to expect it to intervene as the attack got underway last month.
Note that in the last days the Syrian and the Russian air force conducted a massive bombing controlled by opponents of the regime of the settlements located in the provinces of Daraa and Quneitra.
The provisions did not elaborate on the implications of the deployment of military units in the zone.
Israel seized 1,200 square kilometres (460 square miles) of the Golan from Syria in 1967 and later annexed it, in a move never recognised internationally.
With a mix of military force and negotiated surrenders, his forces this month captured more than 90 percent of Daraa, the southern province where protests against him first erupted in 2011.More news: Boeing gets $3.9 billion contract for new Air Force One jets
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The Russian-backed offensive has advanced swiftly, unopposed by President Bashar al-Assad's foreign adversaries.
They say the intensity of the bombardment has forced rebels in many towns to sign surrender deals that offer safe passage to those who want to move to other opposition areas after handing over their weapons, while enlisting those who stay into the military.
With the city of Daraa and most of the province under their control, government forces have turned their focus to the area near the frontier with Israel, to clear the last pockets of the opposition. This has encouraged displaced civilians to return in droves to Nawa, said a local activist who goes by the name Selma Mohammed.
But the talks faltered, triggering the overnight onslaught and a new wave of displacement, with hundreds leaving the town again.
Starting early Wednesday, a series of barricades on the road leading into the town were removed to let dozens of vehicles in, an AFP correspondent there said. Capturing Nawa would enable them to advance on militants in the area linked to the Islamic State group.
The offensive has displaced more than 230,000 people, many of them on the run in the open from the onslaught.
In the border march, Moaz al-Assaad, a photographer in Quneitra, said by the time he made it to the frontier with Israel, the protesters had dispersed. The deal, concluded after the 1973 Middle East war, created a buffer zone patrolled by the U.N. Disengagement and Observer Force.