Israel has said it will not allow sophisticated weapons to flow from Syria to the Iranian-supported Hezbollah. Since the Syrian war broke out, Israel has carried out a series of airstrikes in Syria that destroyed weapons shipments believed to be headed to Hezbollah.
While the Israel and Syria have largely refrained from direct confrontation since the 1973 Mideast war, Israel has shown a readiness to act.
In 2007, Israeli warplanes bombed a suspected nuclear reactor in Syria, and on two previous occasions, Israeli warplanes buzzed over Assad's palace in a show of strength. In 2003, Israel also bombed a training camp belonging to a Syrian-backed militant group that had carried out a suicide bombing in Israel.
Israel also remains concerned that an ouster of Assad could see power in Syria fall to Islamic militants there, particularly al-Qaida-linked groups, and further destabilize the region.
Israeli analyst Ephraim Kam said neither Syria nor Israel want war, and that Hezbollah and Israel are interested in only limited confrontations.
"What can Israel achieve by going to war?" asked Kam, a researcher at the Israeli Institute for National Security Studies. "Syria is not in a position to go to war now, with civil war taking place."
Associated Press writers Albert Aji in Damascus, Syria, and Bassem Mroue in Beirut contributed to this report.
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