Syria warned Thursday of a possible “surprise” response to an Israeli air raid  on an alleged military research center, as it lodged a complaint with the United Nations regarding the attack.
Damascus could take "a surprise decision to respond to the aggression of the Israeli warplanes," Syrian ambassador to Lebanon Ali Abdul-Karim Ali said a day after Israel struck against Syria.
"Syria is engaged in defending its sovereignty and its land," Ali told a website of the Lebanese militant group Hezbollah .
Syria said it complained to the United Nations, even though it is still technically at war with the Jewish state.
State news agency SANA  said the foreign ministry's complaint evoked a 1974 disengagement agreement.
"The Ministry of Foreign Affairs has summoned Iqbal Singha, commander of the UN Observer Disengagement Observer Force... and informed him of an official protest over the Israeli violation of the disengagement agreement of 1974," the ministry said.
Israel maintained a stony silence over Syria's claims, as well as over separate reports from security sources that its jets had struck a weapons convoy near the Lebanon border, despite a growing chorus of international condemnation.
Iranian deputy foreign minister Hossein Amir Abdollahian warned of severe fallout.
Without elaborating, he said the "Zionist regime's attack on the outskirts of Damascus will have grave consequences," in remarks reported by the Isna news agency.
In the past, Iran has said that any Israeli attack on Syria would be considered an attack on the Islamic republic.
Hezbollah, Assad’s closest ally in Lebanon, said Wednesday's attack "fully unmasked what has been happening in Syria over the past two years and the criminal objectives of destroying this country and weakening its army."
Russia also condemned the attack, warning that any Israeli air strike against Syria would be "unacceptable."
"If this information is confirmed, then we are dealing with unprovoked strikes against targets located on the territory of a sovereign state, which brazenly infringes on the UN Charter and is unacceptable, no matter the motive used for its justification," said a ministry statement.
In Cairo, Arab League chief Nabil al-Arabi condemned the "Israeli aggression," saying in a statement that it violated the territory of a sovereign Arab state.
"Israeli fighter jets violated our airspace at dawn today and carried out a direct strike on a scientific research center in charge of raising our level of resistance and self-defense," the general command said.
The warplanes entered Syria's airspace at low altitude and under the radar, the army said, adding that two site workers were killed.
On the political front, Syria's main opposition group was to meet Thursday in Cairo, a day after a surprise statement from its chief that he was willing to hold talks with regime officials, a Syrian National Coalition member said.
"This meeting was organized well before the Syrian National Coalition leader, Moaz al-Khatib, made his statement," SNC member Samir Nashar told AFP.
Khatib announced on Facebook on Wednesday that he was "ready for direct discussions with representatives of the Syrian regime in Cairo, Tunis or Istanbul."
He laid down as conditions the release of "160,000 detainees" and that the passports of exiled citizens be renewed in embassies abroad.
The United Nations says a total of more than 60,000 people have been killed in the country's 22-month conflict .