CAIRO/WASHINGTON/RAFAH, Gaza Strip (Reuters) -Palestinian militant group Hamas said on Wednesday it was unwilling to make more concessions to Israel in negotiations over a ceasefire for Gaza, although talks were still under way in Cairo aimed at pausing Israel's seven-month-old offensive. Israel continued tank and aerial strikes on the southern Gaza city of Rafah on Wednesday and has threatened a major assault on it. Its forces moved in via the Rafah border crossing with Egypt on Tuesday, cutting off a vital aid route and the only exit for the evacuation of wounded patients.