GAZA CITY, Palestinian Territories: Israeli warplanes and tanks hammered Gaza Friday, killing nine people in the deadliest day of violence in the Strip since the end of the Gaza war two years ago. And a truce declared by Palestinian armed groups unravelled even before it could take hold as they fired dozens of mortar rounds and rockets into southern Israel. The latest deaths came after 24 hours of deadly tit-for-tat violence that began Thursday when Hamas militants fired an anti-tank missile at an Israeli school bus, critically wounding a teenager and lightly injuring the driver. “The attack on a school bus yesterday crossed the line ... Whoever tries to hurt and murder children, his blood will be on his own head,” Israeli Prime Minister Benjamin Netanyahu said in Prague Friday before heading home. Since the bus attack, Israel has launched more than 20 raids on targets across the enclave. By Friday afternoon, it had had killed 14 Gazans — including seven civilians, among them a 10-year-old boy, five Hamas militants and one policeman. It was not immediately clear if another person killed was a combatant or a bystander. At least 57 Palestinians were wounded, 12 of them seriously, medics said. The toll of nine dead made this the deadliest day in Gaza since the end of Operation Cast Lead, the devastating 22-day offensive Israel launched in December 2008 that claimed the lives of some 1,400 Palestinians, more than half of them civilians, and 13 Israelis, 10 of them soldiers. In the wake of the strikes, the self-declared truce called by Hamas appeared meaningless, with both Hamas and Islamic Jihad claiming mortar and rocket attacks on Israel Friday. “Our ... warriors are ready to react to the Zionist aggression and respond to any foolish acts committed by the occupation with everything they have,” said a statement from Hamas's armed wing, the Ezzedine Al-Qassam Brigades. A statement on the group's website also said the “resistance” had fired several Grad rockets at Ashkelon and that smoke was rising from the Israeli city. — Agence France-PresseHowever, the Israeli defense ministry said its Iron Dome anti-missile system had intercepted three of the rockets, while a fourth struck open ground without causing damage. Two of Friday's deadliest strikes took place around the southern city of Khan Yunis, with one killing two Hamas militants just east of the city. A second hit a group of civilians slightly farther north, killing a man in his 50s and a woman and her 21-year-old daughter, medics said. Four others were wounded in that raid, including an 18-year-old girl who was in serious condition. The Israeli military said it had targeted “two terrorist squads at the launch sites” and expressed regret for harming civilian bystanders. However, a military statement blamed Hamas for choosing “to operate from within its civilian population, using it as a human shield.” Another missile strike killed one Hamas militant near the northern town of Beit Lahiya, while a second militant died later of his wounds, Hamas said. Witnesses had reported seeing several men trying to fire a rocket from the area. As dusk fell, a shell slammed into a cemetery in the Shejaiya neighborhood of Gaza City, killing two people, one of them a 10-year-old boy, and wounding 10 others, some of them also children, medics said. The military had no immediate comment. In addition to the anti-tank missile, militants on Thursday lobbed more than 50 mortar rounds at Israel, one of which hit a house. More than 30 more were fired Friday, police and media reports said. The bus attack was the first time an anti-tank missile had hit a civilian target in Israel, and was seen by the Jewish state as a worrying escalation. Hamas said it was in revenge for three of its operatives killed in an air strike Saturday, which the army said targeted militants planning to kidnap Israelis from Sinai during the upcoming Passover holiday. The bus attack drew strong condemnation from Washington, Europe and the United Nations. As the dust settled after a day of attacks and counter strikes, both sides were mulling their options, aware that the escalating violence could rapidly deteriorate into all-out war.