DOHA/CAIRO/JERUSALEM, Jan 16 (Reuters) - Israel airstrikes killed at least 77 people in Gaza overnight on Thursday, residents and authorities in the enclave said, hours after a ceasefire and hostage release deal was announced to bring an end to 15 months of war between Israel and Hamas.

The complex ceasefire accord emerged on Wednesday after mediation by Qatar, Egypt and the U.S. to stop the war that has devastated the coastal territory and inflamed the Middle East.

The deal, scheduled to be implemented from Sunday, outlines a six-week initial ceasefire with the gradual withdrawal of Israeli forces from the Gaza Strip, where tens of thousands have been killed. Hostages taken by militant group Hamas, which controls the enclave, would be freed in exchange for Palestinian prisoners detained in Israel.