Heavy Russian attacks reported after rebels try to obstruct Syrian government bid to retake strategic border crossing.
Russia’s military has carried out waves of air strikes in recent days on rebel-held areas of the southern Syrian city of Deraa, say anti-government fighters and witnesses.
Russian jets targeted rebel-held areas of Deraa for two days after Syrian opposition groups on Sunday stormed the heavily garrisoned Manshiya district in a campaign that sought to obstruct any army attempts to capture a strategic border crossing with Jordan from the opposition.
A rebel source said that there were at least 30 Russian sorties on Tuesday, thwarting further rebel gains in the heavily defended enclave that had allowed them so far to secure significant parts of the Manshiya.
"When the regime began to lose control of some areas ... the Russian jets began their operations," said Ibrahim Abdullah, a senior rebel commander.
Al Jazeera could not independently confirm the reported Russian assault.
The army’s control of the rebel-held crossing and chunks of territory in the southern strip of Deraa would sever the rebel link between the eastern and west parts of the province.
The Syrian army said the "terrorists" had failed to make gains and its troops had inflicted many casualties.
The opposition fighters are drawn from both moderate Free Syrian Army groups and members of a newly formed alliance - Tahrir al-Sham.
The fighting spread across other parts of Deraa as rebels fired mortars on government-controlled parts of the province.
Ground-to-ground missiles were also deployed from army barracks to hit rebel-held quarters of Deraa, residents said.
The battles inside the city are the most intense since an alliance of mainstream rebels, known as the Southern Front, who are backed by western and Arab foes of President Bashar al-Assad, launched an unsuccessful large-scale military campaign to capture the whole city in 2015.
The Syrian army has so far failed to recapture the border crossing, a once thriving passenger and commercial gateway with Jordan, despite repeated efforts.
At least half of the southern province is in the hands of FSA fighters but groups affiliated with the Islamic State of Iraq and the Levant group (ISIL) have a foothold in an area to the west of Deraa in the Wadi Yarmouk area, near the Golan Heights.
Aid workers said fighter jets hit a western-funded field hospital in Deraa and raids killed at least seven members of one family in the border area, where many residents fled in the early days of the Syrian conflict.
The Washington-based International Rescue Committee, which supports the hospital that was targeted, said in a statement that four health workers were injured in the attack.
Talks in Astana
The fighting in Deraa comes against a backdrop of renewed diplomatic activity.
Russia, Turkey and Iran are hosting the second round of talks in Kazakhstan’s capital, Astana, on extending the Syrian ceasefire.
Syria’s opposition delegation said it received a commitment from the Russians that they would immediately halt their air strikes on areas held by the opposition.
The head of the Syrian government delegation blamed rebel negotiators for a lack of overall progress after they arrived late to the talks.
Haid Haid, an associate fellow with the Middle East and North Africa Programme at the London-based Chatham House, says the prospects of the talks achieving any real solution to the Syrian conflict are lacking due to virtually "no common ground between Turkey, Russia and Iran".
Speaking to Al Jazeera, he said: "In order to implement the ceasefire, they have to punish those who violate ceasefires.
"And Russia and Iran do not want to put any pressure on the Syrian regime ... There are no enforcement mechanisms that could be a stepping stone to a political solution."
Five years since the conflict began, more than 450,000 Syrians have been killed in the fighting, more than a million injured and over 12 million Syrians - half the country’s prewar population - have been displaced from their homes.