The military airport of Mazze, in the west suburbs of Damascus, was hit by a "possible Israeli missile, which hit a munitions store setting off successive explosions", the head of the Syrian Observatory for Human Rights Rami Abdel Rahmane told AFP.
Lebanese residents in areas north of the capital, Beirut, reported hearing jets overhead before sunset.
The Syrian government accused Israel of striking a weapons research facility in Masyaf, near Wadi Ayoun, in July.
A Syrian military source said the Mazzeh airbase "was not the target of Israeli aggression", according to the official SANA news agency.
The official said Tuesday's alleged airstrikes were not included in the tally. Russians mediated for safe transportation to their new destination.
Russia, another Syria ally, and Damascus have also said that western countries are preparing to carry out strikes against Syria ahead of the Idlib offensive. The Observatory said 13 people were killed.
In the statement from the Syrian president's office, Mr Assad and Mr Zarif said that resorting to "threats and pressure reflect the failure of those countries to realise their plans for the region after Syria and Iran confronted them".
Northwestern Idlib province is the final major swathe of rebel-held territory left standing in Syria after a series of sweeping pro-government offensives earlier this year saw the Syrian government reassert control over the majority of the country.
An attack against the Syrian province's almost 3 million people, he said, would cause "a humanitarian catastrophe".
Mr Pompeo retweeted the United States president's remarks about Idlib.
The UN's Syria envoy Staffan de Mistura described those talks as "crucial" to avoiding an assault, and noted that media reports have suggested Damascus plans to launch an attack next week if a solution is not found.
"Let's try to avoid that the last probably major battle of the Syrian territorial conflict. ends in a bloodbath", he told reporters in Geneva, insisting Russian Federation and Turkey held "the key for the soft solution to the Idlib issue".
But the situation in Idlib has escalated with the presence of ultra-radical groups such as the LLC, which also prevents other rebel factions from accepting a reconciliation deal with the Syrian government.
Damascus's main sponsor Russian Federation has been sounding the war drums in recent days, all the while seeking to pressure Turkey into reining in jihadists in Idlib.
Iranian foreign minister pointed to a trilateral summit between the presidents of Iran, Turkey and Russian Federation which is slated to be held on September 7 in Tehran, saying "ways to confront extremist and terrorist groups, including the Tahrir al-Sham (Jabhat al-Nusra) will be discussed in the meeting".
Thousands of government troops and allied fighters have been massing in areas surrounding the province.
Tuesday's bombardment hit several areas held by the jihadist-led Hayat Tahrir al-Sham alliance, among them the large town of Jisr al-Shughur, but also areas held by rival Turkish-backed rebels, including the town of Ariha.
U.S. officials have grown anxious that an assault on Idlib could involve the use of chemical weapons if the rebels are able to slow regime advances.
The U.S. has twice struck Syrian military installations in response to alleged poison gas attacks.
With rebels defeated in most of Syria, the offensive in the northern province could prove to be the last major battle of the Syrian civil war.
"Just to speak out with some warnings, without taking into account the very unsafe, negative potential for the whole situation in Syria, is probably not a full, comprehensive approach", Kremlin spokesman Dmitry Peskov Peskov said.
"Just to speak out with some warnings, without taking into account the very unsafe, negative potential for the whole situation in Syria, is probably not a full, comprehensive approach", Kremlin spokesman Dmitry Peskov said, apparently in reference to Trump's comment.
Antonio Guterres, U.N. secretary-general, urged Syria and its allies, which include Russia, Turkey and Iran, "to exercise restraint and to prioritize the protection of civilians". He acknowledged that "terrorists" are present in the city, but stressed that an all-out assault is unwise, notably because it would badly affect civilians.
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