Syrian air defences engaged an "enemy target" near the border with Lebanon, west of Damascus overnight, state news agency SANA reported on Saturday.
"Our air defences confronted an enemy target that penetrated airspace above the area of Deir al-Ashair in the Damascus countryside," SANA said.
The Syrian Observatory for Human Rights said air defences reacted to "targets aiming at regime and loyalist positions in Deir al-Ashair" near the Lebanese border.
The Britain-based monitor, which relies on sources inside Syria for its information, did not specify who was responsible for the attack
Lebanese Shiite militant group Hezbollah, which has been backing the Damascus government in Syria's seven-year civil war, operates extensively in the mountainous area between Lebanon and Syria
The Russia-backed government often accuses Israel of targeting its military positions.
Israel has carried out numerous raids in recent years, targeting government forces and their allies from Iran and Hezbollah.
Opinion: Idlib could be the endgame of the Syrian conflict
Asma Al Assad diagnosed with breast cancer
Was Israel behind the killing of a Syria's rocket scientist?
Last week, Syrian air defences confronted another "enemy attack" west of Damascus. As with the latest incident, the Observatory said it was unable to determine who was responsible then as well.
Last month, Syria accused Israel of bombing a military post in the northern province of Aleppo, where the Observatory reported at least nine pro-regime fighters died.
The Observatory also reported that Russia’s main airbase in Syria, located in the regime stronghold of Latakia on the north-western coast, came under a second day of drone attacks Friday.
Images shared on social media showed a number of rudimentary unmanned aerial vehicles that had reportedly been shot down or crashed near the Hmeimim Airbase in Jableh in Latakia’s countryside. The National couldn’t independently verify that the images were genuine.
The Syrian Observatory reported that this was the 18th drone attack on the airfield in 2018.
It reportedly came just 36-hours after a drone attack on the regime’s Al Shayrat airbase near Homs in western Syria where several explosions were heard. There is no indication of casualties or damage to the facility.
Meanwhile, Government airstrikes on opposition-held territory in northwest Syria killed at least 22 people, a monitoring group said Friday, as the U.N.'s children's agency warned a new battle in the war-torn country could affect the lives of 1 million children.
Government forces unleashed a wave of airstrikes across Idlib, Aleppo and Hama provinces after days of building up ground forces at the edge of opposition territory, the Syrian Observatory said.
The group said 14 people were killed in the Aleppo province and another eight in the province of Idlib.
Fears have been building for days of a government offensive against the last major bastion for the opposition, centred in the Idlib province and along the edges of the Aleppo and Hama provinces.
U.N. agencies are warning a campaign to capture Idlib would aggravate an already dire humanitarian situation.
Food, water and medicine are already in short supply in the largely rural Idlib province, which is now home to over 1 million Syrians displaced from their homes by government offensives in other parts of the country, said UNICEF, the U.N. children's agency.
Some 350,000 children, many already living in refugee camps, are at risk of displacement in the event of war, said the agency.
The UNICEF statement said that across Idlib "there are more than 1 million children: exhausted of war, fearful of uncertainty, violence and further displacement."
A local search-and-rescue group said in an initial report on the airstrikes that at least one child had been killed.
The Civil Defence, also known as the White Helmets, said government aircraft bombed homes in the towns of Khan Sheikhoun, Altmana, Sukayk and Alteh.
Hussein Kayal, a media activist in Khan Sheikhoun, said the attack was sudden and shattered nearly three months of calm in the town, as the government focused on defeating opposition forces in south Syria.
"It's been three hours of non-stop bombing," he said.
Syria's government dropped leaflets across the province Thursday, urging residents to reconcile with its rule. Officials have warned that government forces will take back the province by force if necessary.
The Observatory also reported that the Turkish backed Syria Liberation Front and hardline Nusra Front groups had arrested at least 250 people accused of supporting reconciliation with Damascus in recent days.
It said the government was moving ground forces to the north in preparation for an all-out assault, including tanks and artillery.
The U.N. has warned the consequences of such a campaign could be catastrophic.
"War cannot be allowed to go to Idlib," said Jan Egeland, a top U.N. humanitarian adviser on Syria.
There are 2.9 million people living in Idlib and surrounding opposition-held areas, according to U.N. estimates.
The U.N. has appealed to Turkey to open its border to refugees, should the Syrian government decide to attack the province, Egeland said.
Turkey, which has established itself as a sponsor of rebels in northern Syria, already hosts some 3.5 million Syrian refugees - the most of any nation. It has also established 12 monitoring posts in Idlib and deployed 1,000 troops in the province.
However, Turkey has sealed its border to new arrivals and numerous refugees attempting to cross the frontier have been shot and killed by border guards.
But Kayal in Khan Sheikhoun said there were doubts the Turkish presence would deter the Syrian government from attacking.
"People here won't be surprised if there's a ground attack. The Turkish points are weak - they won't repel anything. We're scared that if anything happens, [the Turkish forces] will pull out immediately," he said.
Syria's civil war has killed at least 400,000 people, according to monitors. More than 11 million - or half of Syria's pre-war population - have been displaced from their homes, according to the U.N., including some 5.6 million who have been made refugees abroad.