BEIRUT (AP) -- Israeli warplanes struck areas in and around the Syrian capital Sunday, setting off a series of explosions as they targeted a shipment of highly accurate, Iranian-made guided missiles believed to be on their way to Lebanon's Hezbollah militant group, officials and activists said.
The attack, the second in three days, signaled a sharp escalation of Israel's involvement in Syria's bloody civil war. Syrian state media reported that Israeli missiles struck a military and scientific research center near Damascus and caused casualties.
An intelligence official in the Middle East, who spoke on condition of anonymity in order to disclose information about a secret military operation to the media, confirmed that Israel launched an airstrike in the Syrian capital early Sunday but did not give more precise details about the location. The target was Fateh-110 missiles, which have precision guidance systems with better aim than anything Hezbollah is known to have in its arsenal, the official told The Associated Press.
The airstrikes come as Washington considers how to respond to indications that the Syrian regime may have used chemical weapons in its civil war. President Barack Obama has described the use of such weapons as a "red line," and the administration is weighing its options -- including possible military action.
Iran, a close ally of the Assad regime, condemned the airstrikes but gave no other hints of a possible stronger response from Tehran.
Israel has said it wants to stay out of the Syrian war, but Prime Minister Benjamin Netanyahu has repeatedly stated the Jewish state would be prepared to take military action to prevent sophisticated weapons from flowing from Syria to Hezbollah or other extremist groups.
Israel and Hezbollah fought a monthlong war in mid-2006 that ended in a stalemate.
Syria's state news agency SANA reported that explosions went off at the Jamraya military and scientific research center near Damascus and said "initial reports point to these explosions being a result of Israeli missiles." SANA said there were casualties but did not give a number.
Damascus-based activist Maath al-Shami said the strikes occurred around 3 a.m. "Damascus shook. The explosion was very, very strong," said al-Shami adding that one of the attacks occurred near the capital's Qasioun mountain that overlooks Damascus.
He said the raid near Qasioun targeted a military position for the elite Republican Guards that is in charge of protecting Damascus, President Bashar Assad's seat of power.
Mohammed Saeed, another activist who lives in the Damascus suburb of Douma, said "the explosions were so strong that earth shook under us." He said the smell of the fire caused by the air raid near Qasioun could be felt miles away.
There has been no official statement from the Syrian military.
The strikes put the Assad regime in a tricky position. If it fails to respond, it looks weak and leaves itself open to such airstrikes becoming a common occurrence. But if it retaliates militarily against Israel, it risks dragging the Jewish state and its powerful military into a broader conflict.
After the airstrikes overnight, Israel's military on Saturday deployed two batteries of its Iron Dome rocket defense system to the country's north. It described the move as part of "ongoing situational assessments."
The Iron Dome protects against short-range rockets. Hezbollah fired thousands of rockets at Israel during the 2006 war, while Israeli warplanes destroyed large areas of south Lebanon.
Amos Yadlin, a former head of Israel's military intelligence, said the strike is a signal to Syria's ally, Tehran, that Israel is serious about the red lines it has set.
"Syria is a very important part in the front that Iran has built. Iran is testing Israel and the U.S. determination in the facing of red lines and what it sees is in clarifies to it that at least some of the players, when they define red lines and they are crossed, take it seriously," he told Army Radio.
In Tehran, Iran's Foreign Ministry spokesman Ramin Mehmanparast condemned an Israeli airstrike against Syria and urged countries in the region to remain united against Israel, according to the semiofficial Fars news agency. The brief statement gave no details.
The Fateh-110, or Conqueror, is a short-range ballistic missile developed by Iran and first put into service in 2002. The Islamic Republic unveiled an upgraded version in 2012 that improved the weapon's accuracy and increased its range to 300 kilometers (185 miles).
Iranian Defense Minister Gen. Ahmad Vahidi said at the time that the solid-fueled missile could strike with pin-point precision, making it the most accurate weapon of its kind in Iran's arsenal.