Israel has few other options than aerially buzzing Syrian President Bashar Assad's palace as it did last week, to apply pressure on the Syrian regime to expel Hamas leaders based in the country, local Syria experts said Sunday. But Israel is also hoping Syria, with its close ties to Hamas, could aid in the release of captured soldier Cpl. Gilad Shalit. Last week's sonic boom above Assad's summer residence in the coastal city of Latakia by Israeli warplanes was an obvious warning, but one that has much roar and little bite, the experts said And in the Arab world, Israel's firing of "shots across the bow" did little more than boost public opinion for another of the region's despotic leaders. Struggling for alternatives, Israel has now sought US assistance, with Defense Minister Amir Peretz urging US Secretary of State Condoleezza Rice over the weekend to pressure Syria for Shalit's speedy release. Israel could use its military superiority to carry out attacks on Syrian soil, said Syria expert Eyal Zisser of Tel Aviv University's Dayan Center, "but then you take the risk of causing an escalation, which Israel doesn't want." Neither side has any interest in turning a quiet border between the two countries into a raging battlefield, he said. But then why risk sending Israeli warplanes on a dangerous mission into enemy territory just to send a message? "You can't not do anything," Zisser said. Israel "wanted to send a message: be careful next time. There are red lines - do not cross them." But if the US has failed in its attempts to pressure Syria to crack down on militant groups operating freely in its territory, Israel has even less chance of doing so, and less leverage, Zisser said. US pressure on the Syrian regime was ineffective because Assad failed to understand the price he would pay, Zisser said, and because he had very little to lose. Without bilateral trade between the two countries, there was nothing at stake. Israeli jets buzzing over Assad's residence is a tactic the Israeli air force has used in the past. Israeli steps against, or within Syria, were to a certain extent dependent on Shalit's welfare, said Yoram Kehati from the Interdisciplinary Center's Institute for Counter-Terrorism. Any harm to Shalit would greatly increase the possibility of an Israeli military action in Syria, he said. And while the US had little chance of influencing Syria, there were other options that might be tried, he said. "The US's hands are tied because they have no contact with Hamas," he said. But Russia has been the only state in contact with all parties in the conflict, he said, pointing out that Russian President Vladimir Putin had recently met with a Hamas contingent, including Khaled Mashaal. Russia also has a close relationship with both Syria and Israel, he added. An Israeli airstrike on the headquarters of a group such as Hamas within Syrian territory would be more realistic, or perhaps an assassination attempt on a leader like Khaled Mashaal, Zisser said. Such attacks were an accepted component of Israel's arsenal, he said. Those plans also have precedents. In retaliation for a suicide bombing at a Haifa restaurant, former prime minister Ariel Sharon sent Israeli warplanes on a bombing run into Syria as recently as October 2003 in a raid that successfully targeted an Islamic Jihad training camp. But a bungled 1997 Mossad assassination attempt on Mashaal in Jordan left Israel with no choice but to release then-Hamas spiritual leader Sheikh Ahmed Yassin in exchange for captured Mossad agents held in a Jordanian jail. And while Assad - an ophthalmologist by trade who became heir to Syria's regime when his elder brother died in a car crash - does not have the iron grip on power that his father had, he nevertheless appears to be fully in control and unlikely to go anywhere soon.