Mikoyan MiG-29 jet fighters of the Strizhi (Swifts) aerobatic team fly in formation during the International Army Games 2016, in Dubrovichi outside Ryazan, Russia, August 5, 2016.

Russian jets pounded rebel-held areas of the Syrian city of Deraa on Tuesday for a second day in the first such intensive bombing campaign since Moscow’s major intervention in Syria more than a year ago, rebels and witnesses said.

Rebel groups on Sunday stormed the heavily-garrisoned Manshiya district in a battle dubbed “Death rather than Humiliation” saying the campaign sought to obstruct any army attempts to capture a strategic border crossing with Jordan.

The army’s control of the rebel held crossing and swatches of territory in the southern strip of the city would sever the rebel link between the eastern and west parts of the city.

The Syrian army said the “terrorists” had failed to make gains and its troops had inflicted many casualties.

State media said the armed insurgents showered civilian districts of the southern city with mortars, wrecking many homes.

The opposition fighters are drawn from both moderate Free Syrian Army groups and members of a newly formed alliance – Tahrir al Sham – spearheaded by a faction that was once al-Qaeda’s official affiliate.

A rebel source said 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.

The fighting also spread across other parts of the city as rebels fired mortars on government controlled parts of the city. Ground-to-ground missiles were also deployed from army barracks to pound rebel held quarters of the city, 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 province that borders both Israel and Jordan has escaped the devastation wreaked by Russia’s aerial bombing of northern Syria after Moscow stepped up its military involvement in Syria 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.

“There is not a single day that passes without the regime trying to make advances,” Salamah Aba Zaid, a resident in Deraa said.

At least half of the southern province is in the hands of Free Syrian Army rebels but groups affiliated with ISIS have a foothold in an area to the west of Deraa in the Wadi Yarmouk area near the Golan Heights.

Aid workers said 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.