GAZA CITY ENCIRCLEDIsraeli troops tightened their encirclement of Gaza City amid continued battles with Hamas militants as airstrikes wreaked havoc around the city, the largest in the tiny Mediterranean territory. Al Jazeera TV reported that a strike late Friday hit a school in Gaza City where many were taking refuge, causing casualties. FEARS OVER NEW FRONTSThroughout the war, Israel and Hezbollah have traded fire almost daily along the Lebanon border, raising fears of a new front opening there. “We are in a high state of readiness in the north, in a very high state of alert,” said Israeli military spokesperson Rear Adm. Daniel Hagari. Israeli military officials said their forces have encircled densely built-up Gaza City and began Friday to launch targeted attacks within the city on militant cells.