Israel's bombardment of Gaza has continued with missile strikes on a Hamas-run TV and radio station.
At least two major explosions hit a media complex in central Gaza City housing the offices of Al Aqsa television and radio. The building also houses offices of a number of Arab satellite television news channels.
A loud explosion was also heard within the Abu Khadra government complex in Gaza City.
The strikes came during a heavy night of bombardment, with Israeli illumination flares and repeated explosions lighting up the Gaza skyline and turning it orange.
They followed a day of heavy Hamas-Israeli fighting in which nine children were killed by a strike on a Gaza park where they were playing, according to Palestinian health chiefs - a tragedy that each side blamed on the other.
Signalling an escalation of Israel's Gaza operation, prime minister Benjamin Netanyahu told Israelis to be ready for a "prolonged" war and the military warned Palestinians in three large neighbourhoods to leave their homes and head immediately for Gaza City.
Israeli tanks also resumed heavy shelling in border areas of Gaza, killing five people, including three children and a 70-year-old woman, and wounding 50 in the town of Jebaliya, which was among the areas warned to evacuate, the Red Crescent said.
Many Jebaliya residents said they did not dare attempt an escape. Sufian Abed Rabbo, 27, said his extended family of 17 had taken refuge under the stairway in their home.
"God help us. We have nothing to do but pray," he said by phone. "I don't know who left and who stayed, but in our street we are all very scared to move."
United Nations secretary general Ban Ki-moon expressed concern about the reports of Israeli forces dropping leaflets over northern Gaza last night warning tens of thousands of residents to evacuate to Gaza City.
"If true, this would have a further devastating humanitarian impact on the beleaguered civilians of those areas of the Gaza Strip, who have already undergone immense suffering in recent days," his spokesman said.
"The United Nations agencies present in Gaza do not have the resources on the ground to cope with, or provide assistance to, an enormous extra influx of desperate people."
The latest bloodshed came despite mounting international calls for a ceasefire and followed failed attempts by both sides to agree to even a lull in fighting of several hours for the start of the three-day Muslim holiday of Eid el-Fitr that marks the end of Ramadan.
The Hamas-run health ministry said 10 people, including nine children under 12, were killed and 46 wounded in the blast at a park in the Shati refugee camp on the outskirts of Gaza City.
Each side blamed the other.
Lt Col Peter Lerner, an Israeli military spokesman, said the explosion was caused when a rocket launched by Gaza militants misfired and landed in the park. Palestinian police and civil defence said an Israeli missile struck as children were playing on a swing set.
After three weeks of bloodshed, both Israel and Hamas are holding out for bigger gains and a ceasefire remains elusive, despite an appeal by the UN Security Council and growing pressure from the United States.
Israel says its troops will not leave Gaza until they have demolished scores of Hamas military tunnels under the border that militants use to infiltrate Israel and smuggle weapons. Hamas says it will not halt violence until it receives international guarantees Gaza's seven-year-old border blockade by Egypt and Israel will be lifted.
Mr Netanyahu defended the Gaza air and ground offensive, saying that "there is no war more just than this".
Israel has said it is defending its citizens against attack from Gaza by hitting Hamas rocket launchers, weapons storage sites and military tunnels. But there is growing US frustration with the mounting number of Palestinian casualties - at least 1,072 killed and 6,450 wounded since July 8 - the vast majority civilians, according to Hamas health officials.
The Israeli military says 52 soldiers have been killed, including four yesterday in a mortar attack on southern Israel. Two Israeli civilians and a Thai citizen working in Israel also died.
US president Barack Obama and secretary of state John Kerry have been pressing Israel to accept an immediate and unconditional humanitarian ceasefire.
Israel accepted an Egyptian call for an unconditional ceasefire early in its Gaza campaign, but Hamas rejected the idea.
Mr Netanyahu said: "We need to be ready for a prolonged campaign. We will continue to act aggressively and responsibly until the mission is completed to protect our citizens, soldiers and children."
Hamas spokesman Sami Abu Zuhri responded defiantly, saying: "His threats do not scare Hamas or the Palestinian people and the occupation will pay the price for the massacres against civilians and children."
Israel's last major Gaza invasion ended in January 2009 after 23 days, a third of that time with troops on the ground. Already, the current ground operation, which began 11 days ago, has lasted longer than the one in 2009.
In recent days, Israeli leaders have debated whether to withdraw from Gaza after the tunnels are demolished or to expand the ground operation to deliver a more painful blow against Hamas.
Those in favour of an escalation say unless Hamas is toppled and disarmed, a new round of Israel-Gaza fighting is inevitable. Opponents say attempting to reoccupy densely-populated Gaza, for even a short period, could quickly entangle Israel politically and militarily and drive up the number of fatalities.
Mr Netanyahu did not indicate which way he was leaning, but he insisted that "preventing the arming of terror groups and demilitarising Gaza must be part of any solution".
For now, ground forces have largely operated on the edges of Gaza. The Israeli military has said it has located 31 tunnels, is aware of the existence of 10 more and has so far demolished close to 20.
The overnight strikes also hit the home of the top Hamas leader in Gaza, Ismail Haniyeh.
"My house is not more valuable than the houses of other people, destroying stones will not break our determination," he said.