GAZA/JERUSALEM - Violence has flared up between Israel and Gaza, with the Israeli air force killing three Palestinians and militants firing rockets deep across the border. The latest fighting erupted on Thursday when an air strike on a car killed two militants, one of them from Gaza's governing Islamist group Hamas, whom Israel accused of planning to send gunmen to attack it through the neighbouring Sinai region of Egypt. Palestinian militants answered Thursday's air strike with a barrage of rockets, some of which landed near Beersheba, a city 35 km (30 miles) from Gaza. No one was hurt. Air-raid sirens summoned residents of southern Israel to shelters. Another Israeli air strike followed before dawn on Friday, hitting a Hamas training camp in Gaza City. The blast flattened a nearby home, killing its owner and wounding his wife and six of their children, two critically, hospital officials said. In a statement voicing regret for the civilian casualties, the military said Palestinian rockets stored next to the camp had stoked the explosion. Hamas accused Israel of a "massacre". "We are pursuing intensive contacts with several Arab and international parties, and we stress the necessity of this aggression being stopped immediately," Ismail Haniyeh, head of the Hamas administration in Gaza, told reporters.