Israeli air strikes and rocket launches from the Gaza Strip stretched into the third day despite talk of a temporary truce.
Israel said it would stop its aerial bombardment of Gaza as Egyptian Prime Minister Hisham Kandil visits the narrow enclave, but Palestinian militants continued to fire rockets toward Israel amid the sounds of Israeli missiles landing in Gaza City.
Sirens wailed today in Jerusalem, one of the holiest cities in the world, as it became a target for the first time in this conflict.
"Of course," one member of a militant group told ABC News, "we wouldn't fire rockets if Israel wasn't killing us."
Israel said that more than 150 sites had been targeted overnight, including weapons depots and rocket-launching sites. About 20,000 Israeli reservists have now been drafted as Israeli troops and tanks mass along the border of the Gaza Strip -- apparent preparations for a ground invasion.
Fighting between the two sides escalated sharply Thursday with the first rocket attack from Gaza on Tel Aviv during this burst of violence. No casualties were reported, but three Israelis died in the country's rocket-scarred south when a projectile slammed into an apartment building. More than 550 rockets have been launched at Israel so far, though the military said that one-third had been intercepted by the anti-missile Iron Dome system.
The last time rockets threatened Tel Aviv was during the 1991 Gulf War when Iraqi President Saddam Hussein fired scud missiles into the city.
The death toll in the densely populated Palestinian territory now stands at 30. They are mostly civilians and include at least six children.
The Israeli Defense Forces and Hamas militants have exchanged verbal jabs over social media. Israel tweeted Thursday through its @idfspokesperson, "We recommend that no Hamas operatives, whether low level or senior leaders, show their faces above ground in the days ahead."
The Israeli Defense Forces Twitter account has gained more than 50,000 followers in the past 24 hours.
Hamas fired back through its account, @AlQassamBrigade, "Our blessed hands will reach your leaders and soldiers wherever they are (You Opened Hell Gates on Yourselves)."
Back in Washington, President Obama has been fielding calls from leaders across the Middle East on the mounting violence.
Aboard Air Force One, White House Press Secretary Jay Carney told reporters Thursday that the administration strongly condemns the ongoing rocket fire from Gaza.
"Hamas claims to have the best interest of the Palestinian people at heart, yet it continues to engage in violence that is counterproductive to the Palestinian cause," Carney said.
Israeli has targeted more than 250 sites across Gaza, which is controlled by Hamas, since the operation dubbed "Pillar of Defense" began Wednesday evening.
The first strike was on Ahmed Jabari, the chief of staff of the military wing of Hamas, the Ezzedeen al-Qassam Brigades.
It was followed by a wave of airstrikes on other militants, buildings and installations, notably launching sites and rockets, which included the long-range Fajar rockets.
Gaza Hamas Prime Minister Ismail Haniyeh vowed revenge for Jabari's death.
"His blood will not be in vain," Haniyeh said.
The last time the region saw this amount of violence was four years ago when Israel conducted air and ground invasions of Gaza. It lasted three weeks and left more than 1,400 people dead.