Syria has vowed to hold Israel and its allies accountable for a suspected Israeli air strike on a Syrian military target near Damascus.
The Syrian foreign ministry sent a letter to the United Nations Thursday, stressing what it called Syria's right to defend its sovereignty and territory. It also filed a complaint about the alleged Israeli attack with a U.N. peacekeeping commander in the Golan Heights.
Israel has neither confirmed nor denied launching any military operation in Syria.
U.N. Secretary-General Ban Ki-moon expressed "grave concern" about the reports of an Israeli air strike but said the world body cannot independently verify what happened. He called on all parties in the region to prevent tensions from escalating and respect each other's territorial integrity.
U.S. and regional security sources say Israeli aircraft on Wednesday hit a Syrian convoy heading toward Lebanon and transporting missiles, likely intended for Lebanese militant group Hezbollah. The White House has warned Syria not to engage in such weapons transfers.
Syrian state media gave a different account of the purported Israeli air strike, saying it targeted the Jamraya military research facility outside Damascus. People living nearby said several rockets hit the complex, causing a fire. Syrian rebels claimed they had fired mortar shells at the facility.
Syrian ambassador to Lebanon Ali Abdul-Karim Ali said Damascus has the "option" of carrying out a "surprise" response to the Israeli attack. He did not elaborate in his remarks to Lebanese website Al-Ahad.
Syrian government allies Iran and Hezbollah also condemned Israel.
Iranian news agencies quoted Deputy Foreign Minister Hossein Amir Abdollahian as saying the attack will have "serious consequences" for Israel's commercial capital of Tel Aviv.
Hezbollah said the strike on Jamraya was part of a plot to "destroy" Syria and prevent Arabs from developing military capabilities for "resistance" against Israel.
Russia, another Syrian ally, expressed serious concern about the incident. A Russian foreign ministry spokesman said that if the reports of an Israeli air strike are confirmed, it would be an "unacceptable" action against a sovereign nation, in violation of the United Nations charter.
Despite its political arm, Hezbollah is considered a terrorist organization by some nations and has among its goals the destruction of Israel.
In recent days, Israeli officials have expressed increasing concern about what they see as a threat of Assad transferring sophisticated arms or chemical weapons to Hezbollah, which fought a month-long war with Israel in 2006. Those officials warned that Hezbollah's acquisition of surface-to-air missiles from Syria would be a “game changer."
Israeli lawmaker Tzahi Hanegbi said Thursday that Israel's preference is for Western powers to control those weapons. But he said the international community is not prepared to take such action, leaving Israel in a "dilemma" that only it knows how to resolve.
Middle East Analyst Riad Kahwaji, director of the Institute for Near East and Gulf Military Analysis, said Wednesday's attack was a warning to Damascus from Israel.
“What we witnessed is the Israeli implementation of a self-declared red line," he said.
Edward Yeranian in Cairo contributed to this report
A U.N. spokesman said the Golan peacekeepers did not observe any Israeli planes flying into Syria. He also said weather conditions were bad at the time of the suspected air strike.