Syria's reticence in blaming Israel for killing arch-terrorist Imad Mughniyeh, despite Hizbullah's claims of having "100 percent proof" that Israel was involved, indicates that the issue is causing some friction between Syria and the Lebanese guerrilla group, according to assessments in Jerusalem. Last month, Syria announced that it was launching an investigation into Mughniyeh's assassination, but has so far not released any findings. This has raised eyebrows in Jerusalem, especially since Hizbullah's Deputy Secretary-General Naim Kassem categorically blamed Israel over the weekend for the February car-bombing. According to these assessments, Kassem's speech would have been a good time for Damascus to come out with some evidence of alleged Israeli involvement - something that did not transpire. Mughniyeh's widow has been quoted as suggesting Syrian involvement, and was quoted by an Italian wire service as saying that "the Syrian traitors assisted in killing my husband. The Syrians' refusal to allow Iranian investigators to probe the assassination proves their involvement in the murder of my husband in Damascus." According to assessments in Jerusalem, Damascus's silence may be an indication that the investigation has revealed information that could be very embarrassing to Syria, such as the involvement of Syrian nationals in the assassination - even if they were not at all connected to the Assad government - or the involvement of agents from other Arab states. If Syria has information linking the assassination to another Arab state, they would likely hold on to that information until after the Arab League summit in Damascus later this week, in order not to do anything to further weaken that conference, according to these assessments. Meanwhile Monday, Defense Minister Ehud Barak said the defense establishment was preparing for the possibility that Hizbullah would attack Israel to avenge Mughniyeh's murder. He said that Israel was currently in a "sensitive period" but would overcome the risks. "We cannot be lightheaded about the possibility of retaliation," Barak said during a tour Monday morning of a West Bank checkpoint. "The defense and intelligence establishments are gearing up, and it's a good idea for Israelis to keep their eyes open in the near future." The 40 days of mourning for Mughniyeh ended on Saturday, and Israel has raised its level of alert worldwide - in embassies and Jewish institutions - out of fear that Hizbullah will avenge last month's assassination by striking a Jewish or Israeli target abroad. Hizbullah leader Sheikh Hassan Nasrallah renewed his vow to retaliate for the death of Mughniyeh. "The one who killed our commander must be punished. The killers must be punished, and they will be punished, God willing," Nasrallah said in a videotaped speech aired during a mass rally in Beirut on Monday to commemorate Mughniyeh. "We will choose the time, place and manner of punishment." While the possibility for war is deemed low, the IDF beefed up its presence along the Lebanese border on Friday, and units were diverted there from training facilities and other operations. Defense officials said that a likely attack by Hizbullah could be the targeting or kidnapping of an Israeli official while abroad. "They will likely do something that will not lead to war but can be considered payback for killing Mughniyeh," one official speculated. Nasrallah said the elimination of Israel was possible since following its withdrawal from southern Lebanon in 2000 and its "defeat" in the 2006 summer war, the "myth" of its "invincible" army had been shattered. "Can Israel be eliminated? Yes and a thousand yeses, Israel can be eliminated," he said. "I want to remind you that an Israeli war is no longer a picnic. An Israeli war has become very costly because there is in Lebanon the strength, will and education of the resistance as well as the blood of the resistance's martyrs," he said, drawing cheers from the crowd, who gathered at a rebuilt complex destroyed during the Second Lebanon War. Nasrallah added that UN-mediated negotiations with Israel for a prisoner swap were continuing. "Although the Israelis have killed the pillar of the resistance, we did not halt the negotiations on a prisoner exchange," he said, disclosing that meetings were recently held with UN mediators. "We will not stop the negotiations ... because we want to achieve one of the aspirations of martyr Imad Mughniyeh, that is, to see our prisoner brothers free among their parents and loved ones," Nasrallah said. AP contributed to this report.