Aerial volleys between Israel and Hamas-led Gaza continued Friday with one rocket landing in a field outside Jerusalem.
Israel responded by calling up additional military reserves and shutting down the main roads around the Gaza Strip.
Air raid sirens wailed through Jerusalem, but Israeli officials said there were no injuries or damage. A statement from Hamas claimed responsibility.
Palestinian and Arab leaders are decrying Israel's offensive.
Palestinians marched through the streets of Gaza City shouting their defiance, while, from the West Bank, Palestinian President Mahmoud Abbas addressed the Palestinian people.
Abbas urged all Palestinians to put aside their differences and unite, though he said he had been unable to contact Hamas leaders.
Israel's Iron Dome missile interception system continued to fire away on Friday, destroying more than 130 rockets. But Israeli Defense Forces [IDF] said more than 330 rockets from Gaza have landed in Israel since Wednesday. Israel also has been massing tanks along the border with Gaza.
Israeli Prime Minister Benjamin Netanyahu said Friday there will be no letdown in Israel's resolve.
"We are of course operating powerfully against the launch of rockets to central Israel and southern Israel. We are prepared, if needed, to broaden the operation in a significant way,'' said Netanyahu.
Israel said that since Wednesday it has targeted 450 of what it called terrorist sites in Gaza.
The two sides have exchanged hundreds of aerial bombardments, leaving three Israelis and at least 20 Palestinians dead.
Egypt said Friday that it hoped to help pave the way for an end to hostilities.
Egyptian Prime Minister Hesham Kandil visited Gaza, promising Egypt "will make every effort and make sacrifices to stop this aggression and to achieve a truce."
Back in Cairo, however, Egyptian President Mohamed Morsi lashed out at what he called the Israeli aggression.
"We see what is happening in Gaza, in terms of aggression and the killing of men, women and children, and blood being shed. This is a very dangerous matter," said Morsi. "And this unacceptable aggression on human beings, on men and women, and this is an issue. I warn them again, and that I confirm again, for those who are carrying out the aggression - that they will never rule over the people of Gaza. We will not leave Gaza on its own. We will not leave Gaza on its own.''
Despite Morsi's harsh words, U.S. President Barack Obama telephoned the Egyptian president Friday to discuss the situation and commend Egypt's efforts to defuse the tensions.
Obama also spoke with Netanyahu. The White House said Netanyahu thanked the United States for helping Israel develop a missile defense system called the Iron Dome. The prime minister said the system has knocked out hundreds of rockets, saving countless Israeli lives.
Israeli Defense Forces spokesman Eytan Buchman said that Israel has put a significant dent in Hamas' ability to strike. But he said the fact that Palestinian rockets are still flying means that not enough has been done and that Israel is ready to expand its operations in Gaza.
"We've reached a point where Hamas is becoming increasingly brazen. They are managing with extensive Iranian assistance to get very advanced weapons, and at some point you have to stop with the restraint and you have to move in and score decisively enough to re-energize the deterrence and change the rules of the game so they know that it's not acceptable," said Buchman. "The fact that we’ve shown restraint for so many years shouldn't mean, ‘Hey, why are you attacking now?’ it should mean, ‘Why didn’t you do this earlier?’ We didn’t do this earlier because the Middle East is a volatile area. And we were trying to deal with the situation in other ways. At this point, after 800 rockets that were fired this year, it just became time to change the situation."
Palestinian representatives have so far not replied to VOA's request for a comment.
Meanwhile, tensions have boiled over into Jerusalem, where Muslim Palestinian worshippers clashed with Israeli police outside of some of Islam's holy sites.
Anger over the Israeli air assault have also sparked protests in Egypt, Lebanon and Jordan, while pro-Israel and pro-Palestinians supporters have faced off in protests in the United States.
Protests also erupted in Turkey, where Prime Minister Recep Tayyip Erdogan accused Israeli leaders of carrying out a pre-election stunt.
"Before this election they [Israel] shot these innocent people in Gaza for reasons they fabricated,'' said Erdogan.
Meanwhile, civilians on both sides of the conflict are being urged to take precautions while emergency supplies are being rushed to affected areas. On Friday, trucks of supplies crossed into Gaza from Egypt.
Saif Allah Imam is with the Egyptian Doctor's Syndicate, which is collaborating with the Egyptian Red Crescent.
"We brought with us five loaded trucks, plus two other truck loads, which we already delivered. As well as the delegation which includes the Egyptian Health delegation of the Ministry of Health and the Syndicate for Egyptian doctors,'' said Imam.
Concern in Israel also spread after two Palestinian rocket attacks hit outside Israel's economic capital of Tel Aviv.
"First I heard the siren. Then I heard the explosive. In the Water. In the water. I saw the water fly in the air,'' said one unidentified male resident who witnessed the rockets attacks.
Palestinian militants issued a statement claiming responsibility for at least one of the attacks, saying they had fired Iranian-made rockets.
Israeli government spokesman Mark Regev said the attacks show why Israel has no choice but to use its military to retaliate.
"The attempt last night by the terrorists in Gaza to launch rockets on Tel Aviv only underscores the danger that the Israeli public faces in this formidable military machine in Gaza," said Regev. "And what the Israeli government is doing today, what the action that we are taking is designed to do, is to remove that threat, to free the Israeli people from this constant threat of rocket launches from the Gaza Strip."
Israel began its military offensive Wednesday using a missile strike to kill the top military commander of Hamas in Gaza. Israel dropped leaflets warning Gazans to stay away from buildings and locations run by the military wing of Hamas.
Hamas vowed revenge and warned that Israel had opened up what it calls "the gates of hell."
Meanwhile, the Palestinian Authority has repeated its call for the U.N. Security Council to take action to end Israeli air raids on Gaza. On Friday, Palestinian President Mahmoud Abbas said U.N. Secretary-General Ban Ki-moon would visit in two to three days.
The head of the secret service in Gaza, Tawfeek Tirawi, has accused Israel of war crimes.