BEIRUT - Heavy regime bombardment of a rebel-held Syrian town on Saturday killed more than 30 people including two medical staff, as a two-year local truce broke down.

The raids attest to intensifying violence in Syria despite international efforts aimed at bolstering a nationwide ceasefire between government forces and non-jihadist rebels.

Saturday's shelling hit the town of Jayrud, 60 kilometres (35 miles) northeast of Damascus, where the army said Islamist militants killed a regime pilot after he was forced to eject on Friday. In a statement, the military had pledged that the attack on its pilot "will not go unpunished".

The Syrian Observatory for Human Rights said Saturday's bombardment of Jayrud was the first there in at least two years. "Prominent figures in Jayrud have had a local truce with the regime for at least two years, and neither fired on each other," Observatory head Rami Abdel Rahman told AFP.

He said artillery fire and air strikes on the town killed at least 31 people including two medics. It was not immediately clear how many were civilians. Anti-regime groups in Jayrud include the Saudi-backed Jaish al-Islam (Army of Islam), the hardline Ahrar al-Sham, and Al-Qaeda affiliate Al-Nusra Front.

Ahrar al-Sham said in an online statement on Saturday it was attacking nearby government positions "in response to warplanes shelling Jayrud". Activists in the town said the head of the local medical centre and several colleagues were killed.

"There have been at least 45 air strikes today. The town's medical centre was hit and its director Amjad al-Danaf was killed," activist Abu Malek al-Jayrudi told AFP via the Internet. He said the town is home to some 60,000 people and that the bombardment had not stopped since early Saturday.

IS push from Manbij

Several government aircraft have been shot down by rebels or crashed because of technical faults since the civil war erupted five years ago. According to the Observatory, three Syrian officers were killed on Friday when their helicopter crashed in the south near territory held by the Islamic State jihadist group.

Abdel Rahman said government forces had recovered the bodies but the cause of the crash remained unclear. Dozens of local truces have been brokered among the myriad of armed groups fighting in Syria's increasingly complex civil war.

But a broader ceasefire between government forces and non-jihadist rebels brokered by Moscow and Washington in February has been repeatedly violated by both sides.

US officials have accused Russia of not doing enough to rein in its ally President Bashar al-Assad, raising particular concern over attacks on Syria's divided second city, Aleppo. On Saturday, two women and a child were killed in regime shelling of the eastern rebel-held Sayf al-Dawla neighbourhood of Aleppo, the Britain-based Observatory said.

It added that the toll in bombardment of another eastern district the previous day had risen to 17 dead including five children. Friday's attack hit a crowded market in the Tariq al-Bab district.

More than 280,000 people have been killed since Syria's conflict began in March 2011 with protests demanding Assad's ouster. Jihadist groups -- such as rivals IS and Al-Nusra -- have shot to prominence as some of the most powerful factions in the war.

IS has faced growing pressure from an alliance of Kurdish and Arab fighters advancing on its bastion town of Manbij in the north. The US-backed Syrian Democratic Forces surrounded Manbij last month and were fighting street battles in the town's southern and western districts.

But on the northern edges of the town, IS put up fierce resistance and pushed SDF fighters back four kilometres (more than two miles) on Saturday, the Observatory said. "They are trying to break the siege on Manbij by pushing from the north and east," Abdel Rahman told AFP.