A volley of rockets has been fired into southern Israel from Gaza, hours after a unilateral Israeli ceasefire began. At least four out of five rockets landed near the town of Sderot, with no reports of injuries. Israel launched an air strike on Gaza in response. The exchange puts an immediate strain on the ceasefire, which followed three weeks of fighting. Israel says its troops will not pull out for now, but Hamas said it would not accept an Israeli presence in Gaza. Nearly 1,200 Palestinians and 13 Israelis have been killed since Israel launched its offensive against Hamas on 27 December. Shortly before the rockets fell, Israeli troops briefly traded fire with Hamas militants in the north of the Gaza Strip after coming under attack, Israeli military officials said. International leaders are due in Egypt on Sunday for a summit aimed at shoring up the ceasefire. Heads of state from across Europe will join Egyptian President Hosni Mubarak, Palestinian Authority leader Mahmoud Abbas and UN chief Ban Ki-moon at Sharm El-Shiekh to give their backing to a permanent peace. Olmert warning The rockets were fired at about 0900 (0700 GMT), […]