Militants in Gaza had fired nearly 1,000 rockets at Israel, the IDF reported. More than 340 had been intercepted, including 41 of the 146 fired Sunday, the military said. Meanwhile, the IDF conducted 130 strikes during the day, it reported.
The IDF, which has been touting the "pinpoint" precision of its airstrikes via Twitter, said it had hit a slew of what it called "terrorist" sites while sparing other damage.
"Terrorists put an underground launch site next to a mosque. We targeted the site. The mosque was unharmed," the IDF said in one post, which was accompanied by military video of the raid.
The Israeli military has also said that nearly 100 rockets fired from Gaza in recent days have crashed back into the strip. "Hamas fires from civilian areas and hits its own people," it said on Twitter.
The Israeli government has called up 75,000 reservists and massed 30,000 troops across the border of the Palestinian territory, the IDF said. In Jerusalem, Israeli Prime Minister Benjamin Netanyahu told reporters that Israel is prepared to significantly escalate its operation against Palestinian militants in Gaza.
"We are exacting a heavy price from Hamas and the (other) terrorist organizations, and IDF is prepared for a significant expansion of its operations," Netanyahu said before his weekly Cabinet meeting.
The fighting has put new strains on Israel's relationship with Egypt, which is attempting to broker a cease-fire. The Muslim Brotherhood-led government that took power in June has pledged to maintain Egypt's peace treaty with Israel -- the cornerstone of what peace has been achieved in the turbulent region -- but sympathy for the Palestinians runs deep among Egyptians.
On Egypt's border with Gaza, about 500 Egyptian protesters crossed into the territory on Sunday in what their leader said was a show of solidarity with the Palestinians. They raised Palestinian flags and chanted, "We are the youth of January 25 revolution, Palestine will be free! Open the crossing, Israel is the enemy!"
"We have broken the siege," said Rami Shaath, the group's main organizer. "The Arab Spring has changed the region. We are happy to go in to support our Palestinian brothers, but it's sad to hear the explosions of the Israeli bombing of Gaza all the way on the Egyptian side. We brought in small amounts medical supplies, food, and water, but our main message is political support to the Gazans."
Arab League Secretary-General Nabil el-Araby and 16 foreign ministers from the league's member states will drive into Gaza on Tuesday for talks, a spokesman for the organization said. Meanwhile, Abbas will hold talks in the West Bank with Tony Blair, the envoy for the Mideast Quartet, and with U.N. Secretary-General Ban Ki-moon during their visits to the region in the coming days, said Saeb Erakat, a member of the PLO's executive committee and an Abbas ally.
The United States and several European countries have put the brunt of the blame for the current crisis on Hamas, an Islamic fundamentalist movement that has been branded a terrorist organization by the United States, Israel and the European Union. Those Western powers say Israel has a right to self-defense, while Arab and Muslim nations have accused Israel of being the aggressor.
Rocket attacks into Israel were the "precipitating event" for the fighting under way now, U.S. President Barack Obama said during a stop in Thailand on Sunday. "We are actively working with all the parties in the region to see if we can end those missiles being fired without further escalation of violence in the region."
Obama said he has spoken with Netanyahu, Egyptian President Mohamed Morsy, and Turkish Prime Minister Tayyip Erdogan. He emphasized that "those who champion the cause of the Palestinians should recognize that if we see a further escalation of the situation in Gaza, then the likelihood" of peace talks resuming that could lead to a two-state solution "is going to be pushed off way into the future," Obama said.