GAZA CITY (AFP) - At least four Gazans, among them children, were killed Tuesday by Israeli fire as tensions between Hamas fighters and Israel soared after days of rocket attacks and air raids. Another 12 people, including young children, were wounded when an Israeli shell slammed into a home in Shejaiya on the eastern outskirts of Gaza City, an emergency services spokesman said. Adham Abu Selmiya said the deaths occurred when Israel "opened fire on young people who were playing football in Shejaiya." The dead, three of whom were cousins, were named as Mohammed al-Helu, 11; Yasser Ahad al-Helu, 16; Yasser Hamad al-Helu, 50 and Mohammed Harara, 20. Four of the injured were in serious condition while the other eight were in moderate condition, Abu Selmiya said. Pictures taken by an AFP correspondent in Gaza City's Shifa hospital showed three small children, a teenager and an adult covered in blood. The killings follow days of rising cross-border violence, which has ramped up tensions between Israel and Gaza's Hamas rulers and once again raised fears of a large-scale Israeli military invasion to stamp out rocket fire. The bloodshed drew an angry response from the armed wing of Hamas, the Ezzedine al-Qassam Brigades, which vowed revenge. "This crime will not go unpunished and the resistance is not afraid of the so-called Zionist deterrence," a Hamas website quoted brigades spokesman Abu Obeid as saying. The Israeli army confirmed it had fired mortar shells at the eastern outskirts of Gaza City shortly after four Qassam rockets hit Israel.