AMMAN - Syrian rebels repelled on Sunday a suicide attack by Islamic State militants on a military base near a border crossing into Iraq and a rebel convoy headed to the base, leaving at least four dead and several injured, rebel sources said.The midnight attack on a heavily defended base near the al Tanf border crossing involved at least one explosive-laden vehicle that rammed an entrance to the base. At least two people were killed and scores wounded, a rebel source said.The militants also staged a suicide attack on a convoy of rebel fighters from the Western-backed Osoud al Sharqiya rebel group, who had sent reinforcements from their outpost near the Rukban refugee camp further south-west. Two of their fighters were killed in the ambush.Islamic State "staged a suicide attack and there were clashes inside Tanf. Two were killed and several injured. They also attacked our convoy but it's over and matters are under control," said a senior rebel source from Osoud al Sharqiya who requested anonymity.