GAZA CITY, Gaza Strip (AP) — A cease-fire agreement between Israel and the Gaza Strip's Hamas rulers took effect tonight, bringing an end to eight days of the fiercest fighting in years and possibly signaling a new era of relations between the bitter enemies. The Egyptian-sponsored deal delivered key achievements for all involved. It promised to halt years of Palestinian rocket attacks on southern Israel and ease border closings that have stifled Gaza's economy, and it affirmed the emergence of Egypt's new Islamist government as a key player in a changing region. But vague language in the agreement and deep hostility between the combatants made it far from certain that the bloodshed would end. News of the truce, announced in Cairo and reached after furious diplomacy that drew in U.S., U.N., European and regional diplomats, set off ecstatic celebrations in Gaza, where thousands poured into the streets, firing guns into the air, honking horns and waving Palestinian, Hamas and Egyptian flags. In Israel, small demonstrations were held in communities that were struck by rockets. Protesters said the military should have hit Hamas harder and some held signs demanding security and denouncing "agreements with terrorists." Leaders on both sides used tough language as they prepared to engage in indirect negotiations on a future border arrangement through Egyptian mediators.