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Dozens of people have been killed in Syrian air strikes on the cities of Idlib and Aleppo and the suburbs of Damascus, according to the Syrian Observatory for Human Rights.

At least three people were killed while 16 others were injured when Syrian helicopters dropped seven barrel bombs on a neighbourhood in Idlib on Monday, the UK-based monitoring network said.

The death toll is expected to rise.

In Aleppo, at least five people, including three children, were killed in air strikes on the city of al-Bab, the Syrian Observatory said.

Ongoing clashes in Aleppo province have left many people dead or injured while thousands have been left homeless.

In the suburbs of Damascus, Zabadani and Eastern Ghouta, 12 barrel bombs were dropped on several areas leaving many injured, the Syrian Observatory said. No death toll has been reported yet.

Al Jazeera could not independently verify the reports of air attacks in Syria.

In central Damascus, a man detonated his explosives on Monday in the Rukn al-Din district, where major security compounds are located, according to a Syrian army source.

The Syrian Observatory said a senior Syrian army officer was wounded in the attack but the military denied the report.

"A major-general who heads the munitions and supply division of the Syrian army was injured [along with two others] and one of his companions was killed in the attack," Rami Abdul Rahman, head of the Syrian Observatory, said.

Army tight-lipped

Ali Ebrahim, a journalist, told Al Jazeera from Damascus over phone that the army was tight-lipped about the incident.

"I spoke to the Syrian army's press office and they refused to talk about it," he said.

"According to my sources, the general has been taken to the hospital and his situation has been stabilised.

"One of his bodyguards has died. There were civilian casualties too."

State-owned TV station Al Ikhbariya said that when authorities stopped an armed group in Rukn al-Din, one member blew himself up.

A Syrian army source rejected the report of the major-general's death,  saying only that one officer was wounded. He said five people involved in a suicide attack in Rukn al-Din had been killed or arrested.

Elsewhere in Syria, clashes have resumed between government forces and opposition fighters in al-Suwaida and al-Hasakah.

Also on Monday, two UN peacekeepers were wounded in the Israel-held Golan Heights by mortar fire coming from the Syria.

A civil defence member holds a rescued schoolgirl after what activists said was a barrel-bomb attack in a residential area of Aleppo [Reuters]

In another Syria-related development, the US military has denied  a report that strikes led by it killed at least 52 civilians in northern Syria earlier this week. It said those killed were actually fighters.

The Syrian Observatory's Abdel Rahman told Al Jazeera that among the 52 civilians killed were children.

He said the toll could rise as rescuers were battling to save 13 people trapped under rubble.

"US Central Command can confirm that coalition forces conducted air strikes in the vicinity of Birmahle, Syria, on April 30, destroying several ISIL fighting positions and striking more than 50 ISIL fighters," Major Curt Kellogg, Central Command spokesperson, said in a statement, referring to the Islamic State of Iraq and the Levant group.

"We currently have no indication that any civilians were killed in these strikes."

He also said Kurdish fighters and Syrian opposition fighters were clashing with ISIL fighters in a town roughly 2km away from Birmahle at the time of the air strikes.

"Prior to the air strikes, Kurdish forces, who held the town before leaving after being attacked by ISIL, reported there were no civilians present in that location and that there had not been any civilians present for two weeks prior to the coalition airstrikes," Kellogg said.

"We have significant mitigation measures in place within the targeting process and during the conduct of operations to reduce the potential risks of collateral damage and civilian casualties.

"We work extremely hard to be precise in the application of our airstrikes and take all allegations of civilian casualties very seriously."

The Syrian Observatory's Abdel Rahman had suggested that Birmahle was inhabited by civilians only, with no ISIL presence.

Infographic Syria: Communities Besieged [Al Jazeera]

Source: Al Jazeera and agencies