Russia bombed rebel-held parts of southern Syria late Saturday for the first time since brokering a ceasefire there nearly a year ago, a monitor group said, as allied regime troops prepare a ground assault.
Southern Syria is a strategic prize for local and global players involved in the country's convoluted seven-year war.
After securing the capital Damascus, Syrian President Bashar al-Assad appears keen to recapture the southern provinces of Daraa and Sweida, still mostly held by rebels.
He has sent military reinforcements there for weeks, dropped flyers demanding rebels surrender, and escalated bombardment in recent days.
Late Saturday night, his Russian allies bombed rebel-held towns in Daraa for the first time since the summer of 2017, said the Syrian Observatory for Human Rights.
"Intense Russian air strikes are hitting towns in Daraa's eastern countryside for the first time since the ceasefire was agreed in southern Syria last year," said Observatory head Rami Abdel Rahman.
The Observatory said the warplanes used Saturday -- based on type, location, munitions and flight patterns -- had come from the Russian-operated Hmeimim base in coastal Syria.
The Britain-based monitor said at least 25 Russian strikes hit the rebel zones but did not have any casualty figures.
- Regime takes two villages -
Russia, the United States, and Jordan agreed in July of last year on a de-escalation zone in rebel-controlled parts of southern Syria that would tamp down hostilities there.
Since then, Moscow's warplanes -- active in Syria since 2015 -- had refrained from bombing rebel positions in the south.
But violence has been ratcheting up this week as Syrian government forces look to retake the south militarily.
Forces loyal to Assad began ramping up their air strikes and artillery fire on the zone on Tuesday.
At least 19 civilians in rebel-held zones have died since then, according to the Observatory.
Several civilians have also been killed in opposition fire on government zones, with state news agency SANA reporting Saturday that two civilians were killed in Daraa city in rebel shelling.
Some 12,000 people have been displaced from Daraa province in recent days, the Observatory said, with many seeking refuge in poorly-equipped displacement camps further west.
The United Nations has warned that growing violence is putting the lives of 750,000 people in rebel parts of the south in danger.
On Saturday, regime forces took two villages in Daraa province, their first ground gains after days of bombardment, the Observatory said.
- Steady thud of strikes -
"The Russian strikes started around 10:30pm local time (1930 GMT) and stopped after midnight," said Ibrahim Mohammad, a media activist in the battered rebel town of Busr al-Harir in Daraa.
He said he and other residents had taken to their basements and bomb shelters as soon as they heard the planes, describing a steady thud of bombardment for nearly two hours.
In an effort to avoid a deadly offensive, international powers are holding talks aimed at reaching a negotiated settlement for Syria's south.
"All sides should seize the opportunity to negotiate a deal for the conditional return of the Syrian state to the south west and avert a military conclusion that, for all sides and the local population, would be a worse outcome," wrote the International Crisis Group think tank last week.
"The US, Russia and Jordan, which brokered a south-western ceasefire in 2017, should urgently extend that truce in preparation for a broader settlement," the report added.
Earlier this month, Assad said contacts were ongoing between Russia, the United States and Israel over the southern front.
"We are giving the political talks a chance, but if they fail, there will be no choice but liberation by force," he said.
The regime has retaken large parts of Syria from the opposition since Russia intervened militarily on its side in 2015.
A Syrian family takes shelter under an empty building with their tent and cows in Daraa, southwestern Syria, after several days of intensified bombardment by Syrian regime forces