By Bassam Masoud and Nidal al-Mughrabi GAZA/CAIRO (Reuters) -Israel sharply stepped up strikes on the Gaza Strip, pounding the length of the Palestinian enclave and killing hundreds in a new, expanded phase of the war that Washington said veered from Israeli promises to do more to protect civilians. 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 collapsed last week and about double the daily figures typically reported since then. With most Gazans now displaced and unable to access any aid, h…