Israeli warplanes killed five militants in Gaza on Saturday, the second day of cross-border violence in which Palestinian fighters have fired dozens of rockets into Israel, both sides said. Fifteen militants in the Gaza Strip have been killed since Friday, Hamas medics said. On Saturday, a gunman was killed in a vehicle near Gaza's border with Egypt. Earlier in the day Israeli jets killed two gunmen on a motorcycle and two others in a pre-dawn attack, officials in Gaza said. The sounds of explosions and rocket fire reverberated across coastal Gaza and southern Israel early on Saturday and Israeli Defense Minister Ehud Barak said its air strikes would continue.