Israel prepared ground troops along the Gaza border on Thursday and Hamas launched rocket barrages at Israel as international calls mounted for an end to the region's fiercest hostilities in years.
One rocket fired from the Palestinian enclave crashed into a building near Israel's commercial capital of Tel Aviv, injuring five Israelis, police said. Sirens blared in cities across southern Israel, sending thousands running for shelters.
In renewed air strikes on Thursday, Israel destroyed a six-storey residential building in the heart of Gaza City. One man was killed by an Israeli missile fired east of Khan Younis in southern Gaza, medics said.
A wave of violence between Jewish Israelis and the country's Arab minority also spread in several Israeli cities, with attacks on synagogues and Arab-Jewish fighting in the streets.
At least 72 people have been killed in Gaza since violence escalated on Monday, medics said, further straining hospitals already under heavy pressure during the Covid-19 pandemic. Seven people have been killed in Israel, its military said.
Israel has prepared combat troops along the Gaza border and was in "various stages of preparing ground operations", a military spokesman said, a move that would recall similar incursions during Israel-Gaza wars in 2014 and 2008-2009.
"The Chief of Staff is inspecting those preparations and providing guidance," Lieutenant Colonel Jonathan Conricus said.
Health authorities in Gaza said they were investigating the deaths of several people overnight who they said may have inhaled poisonous gas. Samples were being examined and they had yet to draw any final conclusions, they said.
Amid fears the violence could spiral further out of control, Washington planned to send an envoy, Hady Amr, for talks with Israel and Palestinians.
US President Joe Biden said he hoped fighting "will be closing down sooner than later". A British minister urged Israel and Hamas to "take a step back" from the escalation.
Israeli Prime Minister Benjamin Netanyahu has vowed to "continue acting to strike at the military capabilities of Hamas" and other Gaza groups. Hamas is regarded as a terrorist group by the United States and Israel.
On Wednesday, Israeli forces killed a senior Hamas commander and bombed several buildings, including high-rises and a bank, which Israel said was linked to the faction's activities.
Hamas signalled defiance, with its leader, Ismail Haniyeh, saying: "The confrontation with the enemy is open-ended."
Jerusalem Tensions, Israeli Strife
Israel launched its offensive after Hamas fired rockets at Jerusalem and Tel Aviv in retaliation for Israeli police clashes with Palestinians near al-Aqsa mosque in East Jerusalem during the Muslim fasting month of Ramadan.
Turkey, whose hosting of Hamas leaders in Istanbul in recent years has contributed to a falling out with Israel, called on Muslim countries to show a united and clear stance over the Israel-Gaza violence.
A Palestinian source said truce efforts by Egypt, Qatar and the United Nations had made no progress to end the violence.
US Secretary of State Antony Blinken phoned Palestinian President Mahmoud Abbas and said Washington "was exerting efforts with all relevant parties to reach calm," the official Palestinian news agency WAFA said. Abbas is a Hamas rival whose authority is limited to the Israeli-occupied West Bank.
The fighting has also touched off strife within Israel, where some in the Arab minority mounted violent pro-Palestinian protests.
Attacks by Jews on Arabs passing by in ethnically mixed areas worsened overnight. One person was in critical condition after being shot by Arabs in the Arab-Jewish town of Lod, where authorities imposed a curfew, police said.
Over 150 arrests were made overnight in Lod and Arab towns in northern Israel, police said.
In Gaza, two multi-storey residential buildings and a tower housing media outlets, including one linked to Hamas, collapsed after Israel urged occupants to evacuate in advance of its air strikes, and another structure was heavily damaged.
Many in Israel also holed up in shelters as waves of rockets hit its heartland, some blown out of the sky by Iron Dome interceptors.
The fatalities in Israel include a soldier killed while patrolling the Gaza border and five six civilians, including two children and an Indian worker, medical authorities said.
Gaza's health ministry said 17 of the people killed in the enclave were children and six were women. The Israeli military said on Thursday that some 400 of 1,600 rockets fired by Gaza factions had fallen short, potentially causing some Palestinian civilian casualties.
The conflict has led to the freezing of talks by Netanyahu's opponents on forming a governing coalition to unseat him after Israel's inconclusive March 23 election.
Although the latest problems in Jerusalem were the immediate trigger for hostilities, Palestinians are frustrated by setbacks to their aspirations for an independent state in recent years.
These include Washington's recognition of disputed Jerusalem as Israel's capital, a US plan to end the conflict that they saw as favourable to Israel and settlement building.