Israel faces international criticism and threats of retaliation after Wednesday's bombing on the Syrian-Lebanese border, with Russia and the Arab League describing it as a violation of Syria's sovereignty. Syria and Iran threatened to respond to the military intervention, which was widely ascribed to Israeli forces.
Warplanes targeted a "scientific research centre" near Damascus, according to Syrian state television. Other reports said a convoy believed to be carrying Russian-made anti-aircraft missiles across the border to Hezbollah in Lebanon was struck. The Israeli military declined to comment on the reports.
A spokesman for the Arab League said the bombing was a "glaring violation" of Syria's sovereignty. The "silence of the international community about Israel's bombing of Syrian sites in the past encouraged it to carry out the new aggression, taking advantage of political and security deterioration in Syria," Nabil al-Arabi, the league's head, said.
The Russian foreign ministry said: "If this information is confirmed, then we are dealing with unprovoked attacks on targets on the territory of a sovereign country, which blatantly violates the UN charter and is unacceptable, no matter the motives to justify it."
Hezbollah, the Lebanese Islamic militia, pledged full solidarity with the Syrian regime, saying Israel had "perpetrated a barbaric attack".
"In line with its inherent spirit of aggression and criminality, and in accordance with its policy of preventing any Arab or Islamic power from developing technological and military capabilities, Israel perpetrated a barbaric attack against a Syrian installation for scientific research on Syrian territory, causing the death of a number of Syrians, the injury of others, and the destruction of the installation," the Hezbollah statement read. Two people were killed and five wounded in the attack, according to Syrian state television.
The Syrian ambassador to Lebanon, Ali Abdul-Karim Ali, said Damascus retained "the option... to retaliate". The Iranian deputy foreign minister, Hossein Amir Abdollahian, was quoted as saying the attack would have significant implications for Tel Aviv, which is within range of Hezbollah rockets.
The US administration was warned of the attack, according to the New York Times.
Israel continued to maintain an official silence on the air strike, following a pattern of previous military interventions attributed to its forces. Some analysts said this was to minimise the likelihood of retaliatory action.
"Clearly someone attacked something on the Syrian-Lebanese border," said military expert Yossi Alpher. "But it's extremely important in these situations that Israel does everything possible to avoid being accredited with these actions. There's a danger of retaliatory action, whether by Syria or Hezbollah."
Alpher said he was "not in the least surprised" by the attack. In the past few days, high-level Israeli emissaries have been despatched to Washington and Moscow, while warnings that weapons, both chemical and conventional, could reach Hezbollah or jihadists inside Syria had become more shrill. "Anyone who puts two and two together is likely to come to this conclusion [that Israel was responsible]," Alpher said.
Gerald Steinberg, of the Begin-Sadat Centre for Strategic Studies, said Israel's political, military and intelligence leadership would have made careful calculations about the risks of retaliation before ordering air strikes. "This is a government that is very focused on rational cost-benefit analyses. There is no question in my mind that they would have calculated the risks. The costs of not acting would be deemed to be greater than the potential repercussions," he said.
Israel, he added, had "not acted nor spoken publicly about the upheaval in Syria for almost two years. If something has changed, it's because something has changed on the ground."
Amid confusion over the target or targets of the air strike, reports suggested that a convoy carrying conventional weapons, most likely Russian-made SA-17 anti-aircraft missiles, from Syria to Hezbollah depots in Lebanon was targeted.
"These are game-changing weapons," said Miri Eisin, a former Israeli military intelligence officer. Syria, she said, had received cutting-edge military hardware from Russia, including anti-tank and anti-aircraft surface-to-air missiles. "These are some of the most advanced technologies. If they go to Hezbollah - a non-state terror actor on Israel's border - that's a game-changer. Then you are going to prefer pre-emptive action."
The pre-dawn air strike on the Syrian-Lebanese border closely followed reports of intensive sorties by Israeli military planes. United Nations forces on the Israel-Lebanon border "recorded a high number of Israeli overflights throughout the day and the night", UN spokesman Andrea Tenenti told the Guardian.
UN forces had no evidence of illegal weapons or increased Hezbollah presence in their area of operations, close to the border with Israel. "We haven't seen any suspicious activities in the south," he said.