Israel said Tuesday its military struck hundreds of targets in the Gaza Strip overnight, hours after Prime Minister Benjamin Netanyahu said his country's forces were "just beginning" to fight back against Hamas militants.
Military spokesperson Richard Hecht said the bodies of 1,500 Hamas fighters had been found in Israeli territory following their incursion Saturday, and that no militants had crossed into Israel since Monday.
The targets of the latest airstrikes included the Rimal neighborhood in Gaza City, home to many Hamas ministries and government buildings.
"What we will do to our enemies in the coming days will reverberate with them for generations," Netanyahu said in an address late Monday.
The Israeli military said it mobilized 300,000 reservists ahead of "going on the offensive" in response to the surprise attack Saturday by Hamas into areas of Israel along the Gaza Strip.
A Hamas military spokesperson threatened that its fighters would kill one of about 150 civilian hostages Hamas is holding any time Israel targets Gaza civilians without warning.
Israeli Defense Minister Yoav Gallant said in a video statement that Israel would implement a "complete siege" on Gaza, cutting the Palestinian territory off from access to electricity, food, water, and gas.
Those comments drew alarm from human rights groups that said collective punishment of people living in Gaza would violate international law.
U.N. Secretary-General Antonio Guterres told reporters that while he recognizes Israel's legitimate security concerns, military operations must be done within humanitarian law. He said civilians must be protected and civilian infrastructure must not be targeted.
"I am deeply distressed by today's announcement that Israel will initiate a complete siege of the Gaza Strip, nothing allowed in - no electricity, food, or fuel," Guterres said.
"The humanitarian situation in Gaza was extremely dire before these hostilities; now it will only deteriorate exponentially."
The death toll Monday rose to at least 900 people in Israel and 687 in Gaza, and that figure is expected to climb. Nearly 6,000 people on both sides were injured.
U.S. President Joe Biden said 11 Americans were among those killed.
The dead in Israel also included people from Argentina, Britain, Cambodia, France, Nepal, Thailand, and Ukraine, officials from those nations said.
Some governments have worked to carry out evacuation flights for their nationals in Israel. South Korea told VOA's Korean service it expected a flight with 300 of its citizens to arrive in Seoul early Wednesday.
The United Nations said more than 187,000 of the 2.3 million people living in Gaza have been internally displaced.
The leaders of Britain, France, Germany, Italy, and the United States issued a joint statement expressing "united support to the State of Israel, and our unequivocal condemnation of Hamas and its appalling acts of terrorism."
"All of us recognize the legitimate aspirations of the Palestinian people and support equal measures of justice and freedom for Israelis and Palestinians alike. But make no mistake: Hamas does not represent those aspirations, and it offers nothing for the Palestinian people other than more terror and bloodshed," the statement said.
Ari Harow, former chief of staff to Netanyahu, told VOA's Deewa service that Israel had no choice when entering the conflict, with Hamas militants attacking one of the holiest days on the Jewish calendar.
"This is not something that Israel had planned for or had wanted," Harow said. "But once we have been dragged into this and once war was declared, the goal is one and very clear, and that is to destroy the terror infrastructure in Gaza forever, to make sure that the people of Israel, the citizens of Israel, don't have to face this type of brutality ever again."
Ukrainian President Volodymyr Zelenskyy drew a parallel between Russia's invasion of his country and the Hamas attack on Israel.
"The same evil and the only difference is that there is a terrorist organization that attacked Israel, and here is a terrorist state that attacked Ukraine," Zelenskyy said in a video address Monday to a NATO parliamentary assembly in Copenhagen.
Gaith al-Omari, senior fellow at the Washington Institute for Near East Policy, told VOA that Russia will try to use the Israel-Hamas conflict to sever international support for Ukraine.
"If Israel conducts the war in a way that minimizes civilian casualties, I believe it will continue having international support," al-Omari said. "Yet however, if they use unreasonable force, then the shift will change. In the meantime, yes, Russia will try to break the consensus. China will also try to break the consensus. This is going to be a test for the U.S. too."