TEL AVIV, Israel >> Israeli soldiers battled Hamas fighters in the streets of Israel’s south on Sunday and exchanged strikes with Lebanon’s Hezbollah militant group in the north, while Israel’s retaliation strikes leveled buildings in Gaza. The prospect of Hezbollah joining the fighting a day after an unprecedented surprise attack from Gaza raised the chances of a broader conflict.

Hamas fighters, backed by a volley of thousands of rockets, broke through barricades around Gaza early Saturday to rampage through nearby communities in Israel. They took captives back into the coastal enclave, including women, children and the elderly, while Israel’s retaliation strikes leveled buildings in Gaza and its prime minister said the country was at war. Israeli media, citing rescue service officials, said at least 300 people were killed, including 26 soldiers.

At least 250 people were killed in Gaza and civilians paid a staggering cost for the violence on both sides. Israeli TV news aired a stream of accounts from the relatives of captive or missing Israelis, who wailed and begged for assistance amid a fog of uncertainty surrounding the fate of their loved ones. In Gaza, residents fled homes near the border to escape Israeli strikes, fleeing deeper inside the territory after warnings in Arabic from the Israeli military.

Israeli Rear Adm. Daniel Hagari told reporters that “hundreds of terrorists” have been killed and dozens captured.

Previous conflicts between Israel and Gaza’s Hamas rulers brought widespread destruction in Gaza and days of rocket fire on Israeli towns. The situation is potentially more volatile now, with Israel’s far-right government stung by the security breach and Palestinians in despair over a never-ending occupation in the West Bank and suffocating blockade of Gaza.

The flare-up on Israel’s northern border also threatened to draw into the battle Hezbollah, a fierce enemy of Israel’s which is backed by Iran and estimated to have tens of thousands of rockets at its disposal. Hezbollah struck Israeli positions in a disputed area along the border with Syria’s Golan Heights, and Israel’s military responded with armed drone strikes on Hezbollah targets in a disputed area where the borders of Israel, Lebanon and Syria meet.

In an assault of startling breadth, Hamas gunmen used explosives to break through the border fence enclosing Gaza, then crossed with motorcycles, pickup trucks, paragliders and speed boats on the coast. They rolled into as many as 22 locations outside the Gaza Strip early Saturday morning, including towns and other communities as far as 15 miles (24 kilometers) from the Gaza border, while Hamas launched thousands of rockets at Israeli cities.

“Israel is waking up this morning to a terrible morning,” said Lt. Col. Richard Hecht, an Israeli military spokesman. “There are a lot of people killed… children, grandmothers, families, bodies.”

On Sunday, the Israeli military said its forces were fighting Hamas incursions in eight places. An Israeli military spokesperson said that two hostage situations had been “resolved,” but did not say whether all the hostages had been rescued alive.

Israel struck 426 targets in Gaza, its military said, flattening residential buildings in giant explosions. That included a 14-story tower that held dozens of apartments as well as Hamas offices in central Gaza City. Israeli forces fired a warning just before.

Among the 256 killed in Gaza were 20 children, and close to 1,800 wounded, the Palestinian Health Ministry said. UNRWA, the United Nations agency for Palestinians, said more than 20,000 Palestinians left Gaza’s border region to head further inside the territory and take refuge in U.N. schools.

Israeli media said at least 300 people were killed and 1,500 wounded in Saturday’s attack, making it the deadliest in Israel in decades. Hamas fighters took an unknown number of civilians and soldiers captive into Gaza and a line of Israelis with missing relatives snaked outside a police station in central Israel to supply investigators with DNA samples and other means that could help identify their family members.

Hezbollah fired dozens of rockets and shells on Sunday at three Israeli positions in the disputed area and Israel’s military fired back using armed drones at the Lebanese areas.

Israel and Hezbollah are archenemies and have fought several wars in the past, the most recent a 34-day conflict in 2006 that left 1,200 dead in Lebanon and 160 in Israeli. Tensions have been simmering along Israel’s northern border for months.

In a televised address Saturday night, Israeli Prime Minister Benjamin Netanyahu said the military will use all of its strength to destroy Hamas’ capabilities. “All the places that Hamas hides in, operates from, we will turn them into ruins,” he added.

“Get out of there now,” he told Gaza residents, who have no way to leave the tiny, overcrowded Mediterranean territory. Gaza’s 2.3 million people have endured a border blockade, enforced to varying degrees by Israel and Egypt, since Hamas militants seized control in 2007.

In Gaza, much of the population was thrown into darkness Saturday night as Israel cut off electricity. Netanyahu’s office said in a statement that Israel would stop supplying electricity, fuel and goods to Gaza.

Before daybreak Sunday, militants fired more rockets from Gaza, hitting a hospital in the Israeli coastal town of Ashkelon, said senior hospital official Tal Bergman. Video provided by Barzilai Medical Center showed a large hole punched into a wall and chunks of debris scattered on the ground of what appeared to be an empty room and a hallway. The military said patients had been evacuated from Barzilai before the strike.

School was canceled across Israel.

The shadowy leader of Hamas’ military wing, Mohammed Deif, said the assault was in response to the 16-year blockade of Gaza, and a series of recent incidents that have brought Israeli-Palestinian tensions to a fever pitch.

Over the past year, Israel’s far-right government has ramped up settlement construction in the occupied West Bank, Israeli settler violence has displaced hundreds of Palestinians there, and tensions have flared around the Al-Aqsa mosque, a flashpoint Jerusalem holy site.

Deif, who does not appear in public, said in a recorded message that the attack was only the start of what he called “Operation Al-Aqsa Storm,” and called on Palestinians from east Jerusalem to northern Israel to join the fight.

Asked by reporters how Hamas had managed to catch the army off guard, Lt. Col. Richard Hecht, an Israeli army spokesman, replied, “That’s a good question.”

The Hamas incursion on Simchat Torah, a normally joyous day when Jews complete the annual cycle of reading the Torah scroll, revived painful memories of the 1973 Mideast war, in which Egypt and Syria launched a surprise attack on Yom Kippur, the holiest day of the Jewish calendar, aiming to take back Israeli-occupied territories.

The comparison sharpened criticism of Netanyahu and his far-right allies, who had campaigned on more aggressive action against threats from Gaza. Political commentators lambasted the government and military over its failure to anticipate what appeared to be a Hamas attack unprecedented in its level of planning and coordination.

The abduction of Israeli civilians and soldiers also raised a particularly thorny issue for Israel, which has a history of making heavily lopsided exchanges to bring captive Israelis home. Israel is holding thousands of Palestinians in its prisons. Hecht confirmed that a “substantial” number of Israelis were abducted Saturday.

A major question now was whether Israel will launch a ground assault into Gaza, a move that in the past has brought intensified casualties. Netanyahu vowed that Hamas “will pay an unprecedented price.” But, he warned, “This war will take time. It will be difficult.”

Israel’s military was bringing four divisions of troops as well as tanks to the Gaza border, joining 31 battalions already in the area, a spokesperson said.

Hamas said it had planned for a potentially long fight. “We are prepared for all options, including all-out war,” the deputy head of the Hamas political bureau, Saleh al-Arouri, told Al-Jazeera TV. “We are ready to do whatever is necessary for the dignity and freedom of our people.”

U.S. President Joe Biden said from the White House that he had spoken with Netanyahu to say the United States “stands with the people of Israel in the face of these terrorist assaults. Israel has the right to defend itself and its people, full stop.”

The attack comes at a time of historic division within Israel over Netanyahu’s proposal to overhaul the judiciary. Mass protests over the plan have sent hundreds of thousands of Israeli demonstrators into the streets and prompted hundreds of military reservists to avoid volunteer duty — turmoil that has raised fears over the military’s battlefield readiness.