Israeli troops and Hamas fighters battled in Gaza on Monday amid tank, artillery and air strikes, as Israel pressed on with its assault on Hamas. The troops exchanged fire with Hamas militants, fighting against the deepest Israeli thrust into Gaza since it unilaterally withdrew from the coastal territory more than three years ago. The most intensive exchanges of fire were reported to be taking place in the north around Jabaliya and Beit Lahiya. alestinian medics said five children were killed in two separate Israeli strikes around Gaza City early on Monday. At least 75 Palestinians have been killed since Saturday, when Israel upped a week-long bombardment of Hamas targets in Gaza by pouring in ground troops into the densely-populated territory. In the same period, at least 517 Palestinians, including 87 children, have been killed and more than 2,500 wounded, according to Gaza medics. Aid groups said the offensive had aggravated a humanitarian crisis for the 1.5 million residents of Gaza, most of whom depend on foreign aid in a territory that Israel has virtually sealed off since Hamas took control in June 2007.