GAZA CITY, Gaza Strip (AP) -- Gaza militants Friday gunned down 18 alleged spies for Israel in an apparent attempt to plug security breaches and deter others, a day after Israel killed three top Hamas military commanders in an airstrike likely guided by collaborators.
In one incident, masked gunmen lined up seven men, their heads covered by bags, along a wall outside a Gaza City mosque and shot them to death in front of hundreds of people, witnesses said. A note pinned on the wall said they had leaked information about the location of tunnels, homes of fighters and rockets that were later struck by Israel.
In Israel, a 4-year-old boy was killed when a mortar shell hit two cars in the parking lot of Nahal Oz, a small farming community near Gaza. Five Israelis were hurt, one seriously, in several rocket strikes, the military said. One rocket damaged a synagogue.
The child's death was bound to raise pressure on Prime Minister Benjamin Netanyahu from an increasingly impatient public to put an end to rocket and mortar fire from Gaza -- something Israel's military has been unable to do after 46 days of fighting with Hamas.
Netanyahu's office said he expressed his condolences and vowed that Hamas would pay a "heavy price."
The Israeli military said in a statement the deadly mortar shell had been fired from next to a U.N. school currently serving as a shelter for displaced Gazans, but then retracted its claim and said the facility in question was run by Hamas. Israel has repeatedly said Hamas uses schools, mosques and residential areas as cover from which to stage attacks, putting civilians at risk by drawing Israeli retaliation.
Chris Gunness, spokesman for the U.N. refugee agency UNRWA, said the agency strongly denied any claim that one of its facilities had been used in the deadly attack.
By early evening, Gaza militants had fired at least 117 rockets and mortar shells at Israel, while Israel carried out at least 35 airstrikes in Gaza, the military said. Palestinian officials in Gaza reported heavy Israeli activity overnight, with an additional 25 airstrikes by 1 a.m.
In a new warning from Israel's military, automated phone messages told Gaza residents that "Hamas has decided to go to war again" and that people must "get away immediately from areas where Hamas conducts terror activities."
At about the same time, an airstrike hit a house in Gaza City, and a huge orange ball of fire from the explosion rose into Gaza's night sky.
At least 45 people were wounded, health officials said. Ayman Sahabani, head of the emergency department at the city's Shifa Hospital, said only a minute passed before the firing of a warning missile and the bombing.
Early Saturday, an Israeli airstrike hit a house in central Gaza, killing a 47-year-old woman and wounding at least seven other people, said Gaza health official Ashraf al-Kidra. Rescuers were searching the rubble for more survivors.
Since Israel-Hamas fighting began July 8, at least 2,092 Palestinians have been killed, al-Kidra said. According to U.N. figures, at least 478 Palestinian children and minors were among the dead, including 320 who were 12 or younger.
On the Israeli side, the boy's killing Friday raised the death toll to 68, including 64 soldiers, three civilians and a Thai worker.
Friday's escalation came three days after Israel-Hamas truce talks collapsed in Cairo.
At the talks, Hamas had rejected an Egyptian proposal under which Israel would gradually ease its border blockade of Gaza in exchange for a period of extended quiet. Hamas said Israel offered nothing specific, and says it will only halt fire if Israel and Egypt agree to open Gaza's borders to trade and travel.
The border blockade was imposed in 2007, after the violent Hamas takeover of Gaza. Israel has said it cannot lift the closure unless Hamas stops trying to smuggle or manufacture weapons and agrees to disarm, a demand the Islamic militants have rejected.
Mahmoud Zahar, a Hamas leader in Gaza, signaled Friday that Hamas would also reject any U.N. Security Council resolution that seeks to disarm the group. Britain, Germany and France are working on a cease-fire resolution that calls for opening Gaza's borders, in exchange for restoring the rule of Western-backed President Mahmoud Abbas' Palestinian Authority in Gaza. Abbas lost control of Gaza in the Hamas takeover.
Zahar wrote in a text message that "Hamas will not accept any international resolutions that try to touch the weapons of the resistance and don't fully lift the blockade."