BEIRUT - Israeli warplanes struck targets in the Syrian capital Sunday for the second time in three days, officials and activists said, unleashing a series of massive explosions and raising fears of possible wider conflict in the region.

The attacks, which Israeli officials said targeted sophisticated, Iranian-made guided missiles believed to be bound for Lebanon's Hezbollah militant group, marked a sharp spike in 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.

Syria's government called the attacks against its territory a "flagrant violation of international law" that has made the Middle East "more dangerous." It said "Israel should know that our people and state do not accept humiliation" and warned Syria has the right "to defend its people by all available means."

The generally muted response was read out by the information minister after an emergency government meeting and appeared to signal that Damascus did not want the situation to escalate.

Instead, it tried to use the strikes to taint the opposition, claiming the attacks were evidence of an alliance between Israel and Islamic extremist groups trying to overthrow President Bashar Assad.

The air raids pose a dilemma for the regime: Failure to respond could make it look weak and open the door to more strikes, but retaliating militarily against Israel would risk dragging the Jewish state and its powerful army into a broader conflict.

The tempo of the new strikes added a dangerous dynamic to the conflict, fueling concerns that events could spin out of control and spark a regional crisis.

Israel's military, possibly bracing for Syrian retaliation, deployed two batteries of its Iron Dome rocket defense system to the north of the country on Sunday. It described the move as part of "ongoing situational assessments."

A senior Israeli official, who spoke on condition of anonymity in order to disclose information about a secret military operation, confirmed that Israel launched an air strike 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 air strikes come as Washington considers how to respond to indications that the Syrian regime may have used chemical weapons in its civil war. President Obama has described the use of such weapons as a "red line," and the administration is weighing its options - including possible military action.

The White House declined for a second day to confirm or comment directly on the air strikes in Syria, but said Obama believes Israel has the right to defend itself against threats from groups like Hezbollah.

"The Israelis are justifiably concerned about the threat posed by Hezbollah obtaining advanced weapons systems, including some long-range missiles" White House spokesman Josh Earnest told reporters aboard Air Force One as Obama traveled to Ohio.

Iran, a close ally of the Assad regime and Hezbollah, condemned the airstrikes, and a senior official hinted at a possible response not from Tehran but rather its proxy, Hezbollah.

Gen. Masoud Jazayeri, assistant to the Iranian chief-of-staff, told Iran's state-run Arabic-language Al-Alam TV that Tehran "will not allow the enemy [Israel] to harm the security of the region" and that "the resistance will retaliate against the Israeli aggression against Syria."

Israel has said it wants to stay out of the Syrian war on its doorstep, 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 have a long history of enmity, and fought a punishing monthlong war in mid-2006. The militant group fired thousands of rockets at Israel, while Israeli warplanes destroyed large areas of southern and eastern Lebanon during a conflict that ended in stalemate.