Israeli warplanes pounded the Gaza Strip for a fourth day Monday, killing four more Palestinians, as a teenager died in a mystery blast, raising the death toll so far to 23.
The latest strike killed a man in his 60s and his daughter in the Jabaliya refugee camp in northern Gaza, a medical spokesman said.
Several hours earlier, a teenager was killed nearby, just outside Beit Lahiya in what the Palestinians claimed was a drone strike.
But the Israeli military said they had not mounted any strikes in the area since the early hours of the morning.
Israeli Prime Minister Benjamin Netanyahu has vowed to continue targeting militants for "as long as necessary" and several hours later, Israeli warplanes carried out at least eight strikes across the territory, targeting a weapons storage facility and five rocket-launching sites across Gaza.
The first deaths were two militants who were killed in strikes around the southern city of Khan Yunis, both of them from the Islamic Jihad group, which identified them as Raafat Abu Eid and Hamada Suleiman Abu Mutlaq, both 24.
Shortly afterwards, a blast killed 15-year-old Nayef Qarmut and wounded six other teenagers, two critically, near Beit Lahiya.
"A drone strike hit a group of students who were walking by empty land on their way to school," emergency services spokesman Adham Abu Selmiya told AFP.
But the Israeli military denied activity in the area at the time, and an AFP correspondent at the scene confirmed there was no sign of an air strike.
"From an initial check, there were no air strikes in the northern Gaza Strip since the early hours of the morning," a military spokesman told AFP.
The latest attack, which hit the nearby Jabaliya refugee camp, killed Mohammed Mustafa Al-Hasumi, 65, and his daughter Faiza, 35, medics said.
The latest deaths brought to 23 the Palestinian toll from a weekend of tit-for-tat violence that began with Israel's killing of a senior militant on Friday afternoon.
Before the latest strike, Abu Selmiya said 73 people had been wounded in 36 Israeli air strikes across the tiny coastal territory.
A spokeswoman for the army said 31 rockets and mortar rounds had hit Israel since midnight (10pm GMT on Sunday), while another seven were intercepted by the Iron Dome air defence system.
Monday's firings raising the total number of rockets and mortar rounds to hit Israel to 143, while another 52 were shot down.
Four people in southern Israel have been injured by rocket fire, reportedly Thai agricultural workers, with the threat prompting the closure of schools in 11 towns and cities across the south.
On a tour of the cities under fire on Sunday, Netanyahu warned the strikes would "continue as long as necessary" and said he had "given orders to strike all those who plan on attacking us."
Islamic Jihad's Al-Quds Brigades, which lost 12 militants over the past four days, has claimed most of the rockets fired at Israel since Friday.
And on Monday, it vowed to continue "jihad and resistance," while taking a sideswipe at Gaza's Hamas rulers, who are seeking Egypt's help to restore calm, and whose armed wing has not been firing rockets at Israel.
"We call on those panting after any calm, whatever its conditions, to direct their messages at the enemy and not the resistance, for there is no calm after today, except based on the conditions of the resistance," a statement said.
The violence kicked off on Friday after Israel killed Zuhair Al-Qaisi, head of the Popular Resistance Committees, prompting militant groups to begin lobbing rockets over the border.
The army said Qaisi was implicated in planning a deadly attack in August 2011 when militants sneaked across the border from Egypt's Sinai Peninsula and killed eight Israelis in the southern Negev desert.
And it said he was suspected of planning a similar attack "in the coming days."
The bloodshed has prompted noises of concern from Brussels and Washington, and on Monday Beijing called on Israel "to stop air raids against Gaza" and on both sides to "stop firing immediately."
But there was no sign a truce was on the horizon.
Hamas spokesman Taher Al-Nunu said on Sunday that the movement was in constant contact with Egypt over the issue but insisted Israel halt its fire first.
"It was the Israeli side who broke down the ceasefire and we need to see them end the escalation before we talk about the ceasefire," he told AFP.
US State Department spokeswoman Victoria Nuland has previously called for calm and strongly condemned rocket fired in retaliation to the death of the Popular Resistance Committees leader.
"We condemn in the strongest terms the rocket fire from Gaza by terrorists into southern Israel in recent days, which has dramatically and dangerously escalated in the past day," she said on Saturday.
"We call on those responsible to take immediate action to stop these cowardly acts," Nuland added.
State Department head Hillary Clinton reportedly told Israeli opposition leader Tzipi Livni in response to the Gaza onslaught that Israel has the right to defend itself.
"The international community must speaking out clearly, in one voice, against terror on the citizens of Israel's south" Livni said in turn, reported the Jerusalem Post.