Israel would "increase both the intensity of the attacks and the rate of attacks," Prime Minister Benjamin Netanyahu said.

At least 30 Palestinians, including 10 children, and three Israelis were killed as tensions in Jerusalem spread west toward the seacoast Tuesday. Israeli airstrikes flattened a multistory apartment building in Gaza and rockets fired from the Gaza Strip reached Tel Aviv in an unusually far-reaching barrage that sent residents of Israel's largest city scrambling into bomb shelters.

The clashes prompted international calls for calm and raised fears that the situation could ignite into a wider conflict, as Israelis and Palestinians promised that their respective campaigns were far from over.

"We’re in the midst of a big operation," Israeli Prime Minister Benjamin Netanyahu said in a statement Tuesday. "We decided that Hamas and Islamic Jihad will pay a heavy price for their aggressive acts; their blood is in their heads. This operation will take time."

Benny Gantz, defense minister and opposition leader, sounded a similar note: "We will restore quiet and security, and we will do so for the long term."

Palestinian Prime Minister Mohammad Shtayyeh called on the United Nations Security Council to intervene to stop "the Israeli aggression against our people."

Ziyad Al-Nakhalah, secretary general of the Islamic Jihad movement, said his group "will continue this battle, and we promise our people that we will not retreat and will continue to resist, God willing."

United Nations Secretary General António Guterres said in a statement that he was "gravely concerned" about the escalation of violence in Gaza, which he said adds "to the heightened tensions and violence in occupied East Jerusalem."

"He is deeply saddened to learn of increasingly large numbers of casualties, including children, from Israeli airstrikes in Gaza, and of Israeli fatalities from rockets launched from Gaza. The Secretary-General’s thoughts are with the families of the victims."

The 13-story residential building in Gaza, containing 80 apartments, was struck Tuesday evening. Reuters reported that it was hit by an Israeli airstrike, and the Israeli military confirmed Tuesday that it struck a multistory building in Gaza's Rimal neighborhood that it said was being used by Hamas.

There were no immediate reports of casualties.

Shortly after, 130 rockets were fired toward Tel Aviv, on Israel’s Mediterranean coast, and its suburbs, Hamas said in a statement. Israel briefly halted all flights at Ben Gurion Airport.

The Israeli military called up 5,000 reservists for active duty.

In Ashkelon, an Israeli city less than 10 miles from Gaza, two people were killed in rocket attacks Tuesday, Israel's Zaka emergency response team said.

Israeli firefighters check out damaged vehicles in the Israeli town of Holon near Tel Aviv, on May 11, 2021, after rockets are launched towards Israel from the Gaza Strip controlled by the Palestinian Hamas movement.Ahmad Gharabli / AFP - Getty Images

Hamas, a militant group that controls the strip and is considered a terrorist organization by Israel and the United States, has launched 480 rockets into Israel from the Gaza Strip, including targeting Jerusalem, according to the Israeli Defense Forces.