By Bassam Masoud and Nidal al-Mughrabi GAZA/CAIRO (Reuters) -Israel sharply increased strikes on the Gaza Strip, pounding the length of the Palestinian enclave and killing hundreds in a new, expanded phase of the war, as Washington again signalled that Israel could do more to protect civilians in the enclave. The Israeli military said on Friday it had struck more than 450 targets in Gaza from land, sea and air over the past 24 hours – the most since a truce with Hamas collapsed last week and about double the daily figures typically reported since. Decrying a “spiralling humanitarian nightmare”…