A ceasefire has been agreed between Israel and Palestinian militants in Gaza after four days of deadly clashes, an Egyptian official says. The official was quoted as saying that the Egyptian-mediated truce took effect at 01:00 local time (23:00 GMT Monday). A Hamas official later confirmed to the BBC that the truce had been agreed. At least 25 Palestinians have died in Israeli air strikes since Friday, reports say. Israel says 35 people were injured in Palestinian rocket attacks. The Egyptian official - who spoke on condition of anonymity - was quoted by Reuters as saying late on Monday that both Israel and Gaza militants had "agreed to end the current operations". Shortly afterwards, the Hamas official confirmed the truce. The official told the BBC that Israel had made an unusual promise to stop targeting militant leaders in Gaza, if rocket attacks on Israel ceased. Israel has not publicly commented on the reported ceasefire. The cross-border violence was triggered by an Israeli air strike on Friday that killed a senior leader of the militant group, the Popular Resistance Committees (PRC), who Israel said had been planning an attack. Militants in Gaza responded quickly by unleashing a barrage of rockets towards southern Israel, triggering further air strikes. Most of those killed in Gaza were militants, but several civilians also died, Palestinian medical sources say. The US has condemned the rocket attacks as "cowardly"; the Arab League called the Israeli air strikes "a massacre". UN Secretary General Ban Ki-moon has expressed grave concern over the flare-up in violence, describing rocket attacks on Israeli civilians as "unacceptable" and urging Israel to "exercise maximum restraint". Islamic Jihad and the PRC - and not Hamas - have said they have been behind the rocket attacks. The increase in violence has alarmed world powers trying to bring peace talks between Palestinians and Israelis back on track.