WEST PALM BEACH, Fla. - US President Barack Obama cited the "ruthless" suicide bus attack in Bulgaria and upheaval in Syria as reasons to fortify support for Israel, telling a re-election campaign event in Florida on Thursday he stood by Israel's side.Departing from his normal stump-speech themes of tax fairness, education and healthcare, the Democratic president described the Bulgaria airport bus bombing that killed five Israeli tourists as "barbaric" and a "ruthless terrorist attack." "I want everybody here to know under my administration, we haven't just preserved the unbreakable bond with Israel, we have strengthened it," Obama told a mainly older audience in Florida, an electoral battleground state with many Jewish voters.Obama is on a two-day campaign tour in Florida, where he and Republican rival Mitt Romney are neck and neck in opinion polls before the Nov. 6 election."This is a moment of great uncertainty in the Middle East, given what's happening in Syria and given what's happening in other places. Now is the time to make sure that we do everything we can to protect Israel's security," Obama told the retirement community in West Palm Beach.Israel has accused Iran of being behind the Bulgaria attack. Obama did not mention Tehran in his remarks or specify how the United States would proceed to boost support further for Israel.Romney, who is set to visit Israel later this month, has criticized Obama's handling of Iran as weak and declared he would not allow it to possess a nuclear weapon, which Tehran denies building.Obama has also drawn criticism from Republicans in Congress and some in the Jewish American community for focusing attention on the Muslim world - for instance with a major speech in Cairo in 2009 - and for not having visited Israel as president.Debbie Wasserman Schultz, chair of the Democratic National Committee and the first Jewish woman to represent Florida in Congress, said on Thursday that Obama had made clear that the strong bond with Israel was "absolutely non-negotiable.""I am proud to stand with this president and support his remarkable, stellar record in support of the US-Israel relationship," she said.