NIDAL al-MUGHRABI, JEFFREY HELLER and ANDREA SHALAL ISRAEL Prime Minister Benjamin Netanyahu vowed to continue fighting against Gaza militants after U.S. President Joe Biden urged him to seek a "de-escalation" yesterday in the 10-day conflict on the path to a ceasefire. An Egyptian security source said the two sides had agreed in principle to a ceasefire after help from mediators, although details were still being negotiated in secret amid public denials of a deal to prevent it from collapsing. Palestinian health officials said that since fighting began on May 10, 227 people had been killed in aerial bombardments that have…