The IDF has raised the level of alert along the northern border with Syria out of fear that President Bashar Assad would launch a strike against Israel in response to a recent IAF buzz of his palace. Syrian military forces, IDF officers confirmed Tuesday, have also gone on high alert, and the assumption in the IDF is that Assad would order a harsh military response if Israel decided to take additional steps against Damascus in relation to the kidnapping of Cpl. Gilad Shalit in the Gaza Strip. The type of response is unknown at this stage, but officers said it could be a missile strike on IDF installations or communities in the North. Another possibility, military sources said, is that Syria would use its proxy - the Hizbullah in Lebanon - to launch an attack against Israel in its place. Prime Minister Ehud Olmert on Tuesday issued a veiled threat against Syria, vowing to strike "those who sponsor" the terrorists in the Gaza Strip who abducted Shalit. Speaking at a business conference in Beersheba, Olmert said he had ordered the IDF to push forward with efforts "to strike terrorists and those who sent them and those who sponsor them," an apparent reference to Syria. "None of them will be immune." On Monday, Defense Minister Amir Peretz issued a similar threat, warning that Assad would be held personally responsible if Shalit was harmed. "We will know how to reach everyone involved in the kidnapping and everyone who is responsible for his fate," Peretz said. Last week, four IAF fighter jets buzzed Assad's summer residence in Latakia, Syria, to try to pressure him to persuade Damascus-based Hamas leader Kahled Meshaal to release Shalit. Senior defense officials said Tuesday that Israel was considering taking additional steps against Syria as part of its overall effort to retrieve the abducted soldier. According to the officials, Syria has raised its level of alert along the border in wake of last week's flyover of Assad's palace and would try to demonstrate military might if Israel took a similar action. Last week, the Northern Command was warned of the flyover before it happened, to give commanders stationed along the border time to prepare for a possible violent Syrian response. AP contributed to this report.