Israeli aircraft and tanks stepped up strikes in southern Gaza overnight, residents said, after it announced plans to pull back some troops, a move the U.S. said signalled a gradual shift to lower intensity operations in the north of the enclave. Israel says the war in Gaza, which has reduced much of the territory to rubble, killing thousands and plunging its 2.3 million people into a humanitarian disaster, has many months to go. But it signalled a new phase in its offensive, with an Israeli official saying on Monday the military would draw down forces inside Gaza this month and shift to a months-long phase of more localised "mopping up" operations.