Israel's military said it had downed a drone along its southern coastline, the first time it encountered such a weapon since its campaign against the Gaza Strip militants began last week.
The drone came from Gaza and was shot down near the southern city of Ashdod, the military said. There was no immediate confirmation from Gaza on the use of the unmanned aircraft.
Since the latest bout of fighting began, militants have fired nearly 1000 rockets at Israel, causing some injuries and damage to property, but no fatalities among Israelis. By contrast, 172 Palestinians have died as a result of Israel's air attacks, the Palestinian Health Ministry says.
But the use of drones with an offensive capacity could potentially inflict significant casualties - something the rockets from Gaza have failed to do, largely because of the success of the military's Iron Dome air defense system in shooting them down.
The military said the drone was launched from Gaza and was shot down in mid-flight by a Patriot surface-to-air missile.
Israeli Prime Minister Benjamin Netanyahu said that the current Israeli operation could last for "a long time" and that the military was prepared "for all possibilities". That includes a wide-ranging Gaza ground operation, which would likely cause heavy casualties in the coastal strip.
But Netanyahu is coming under increasing international pressure to end the operation soon. UN Secretary-General Ban Ki Moon called for an immediate cease-fire while US Secretary of State John Kerry voiced American "readiness" to help restore calm. Egypt, a key mediator between Israel and Hamas, continued to work behind the scenes to stop the conflict.
Hamas has sent signals it may be ready to consider a cease-fire but appears to be waiting for some tangible military or diplomatic achievement before moving ahead on that front. For his part, Netanyahu wants to show the Israeli public that he has succeeded in significantly degrading Hamas's ability to strike at its Israeli targets before moving ahead diplomatically.
Thousands of Palestinian residents of the northern Gaza Strip fled their homes and sought safety in UN shelters yesterday, heeding warnings from the Israeli military about plans to bomb the area in an offensive against Hamas.
The Israeli air force dropped leaflets around the northern Gaza town of Beit Lahia ordering people to evacuate their homes. Israel says much of the rocket fire has come from the area.
The UN refugee agency for Palestinians, UNRWA, said about 17,000 Palestinians had headed to special shelters set up in 20 United Nations schools in Gaza.
Some raced by in pick-up trucks, waving white flags. "Once we received the message, we felt scared to stay in our homes. We want to leave," said one resident, Mohammed Abu Halemah.
Shortly before nightfall local time, Israel carried out a series of airstrikes in Beit Lahia. Hamas' Al-Aqsa TV station reported four airstrikes in a 10-minute span.
The army says its targets include senior Hamas activists and their homes. Despite Israeli claims that it has inflicted heavy damage on the group, Hamas says it is largely unscathed, and Palestinian medics say most of the dead have been civilians.
However, the UN Office for Humanitarian Affairs said that civilians made up the majority of Palestinian casualties over the past six days - 133 killed and nearly half of more than 1100 wounded.
Israel accuses Hamas of using Gaza's civilians as human shields. "The leadership of Hamas and the other organisations has chosen - at a time when they are using the population of Gaza as human shields - to hide underground, to flee abroad and to deliberately put civilians in the line of fire," Netanyahu said.