JERUSALEM (AP) — Israel’s defense minister announced that the Hamas militant group has started a war against Israel and pledged that “Israel will win.”

Following a security cabinet meeting at the Israeli military headquarters in Tel Aviv, Defense Minister Yoav Gallant warned that Hamas “made a grave mistake” in launching barrages of rockets into southern and central Israel in its surprise morning attack.

In one of the most serious escalations in years between Israel and the militant group that rules Gaza, Hamas gunmen crossed the border fence at several places and infiltrated Israeli communities.

“The state of Israel will win this war,” Gallant said.

THIS IS A BREAKING NEWS UPDATE. AP’s earlier story follows below.

JERUSALEM (AP) — Palestinian militants in the Gaza Strip carried out an unprecedented infiltration Saturday into southern Israel, sending fighters across the border and firing thousands of rockets into the country as the ruling Hamas militant group announced the beginning of a new operation.

The Israeli military put the country on war alert and began striking targets in Gaza in response, setting the stage for what was likely to be a new heavy round of fighting between the bitter enemies. In a serious escalation, salvos of rockets fired from Gaza set off constant air raid sirens as far north as Jerusalem.

Videos posted on social media showed what appeared to be uniformed Palestinian gunmen inside the Israeli border town of Sderot.

A video from Gaza showed what looked like the lifeless body of an Israeli soldier being trampled by an angry crowd of Palestinians shouting “God is Great.” Other footage appeared to show Palestinian militants dragging away an Israeli soldier, still alive, on a motorcycle and Palestinian men dancing atop an Israeli tank that had been set ablaze. The authenticity of the videos could not immediately be verified.

The elusive leader of Hamas’ military wing, Mohammed Deif, announced the beginning of what he called “Operation Al-Aqsa Storm.”

“Today the people are regaining their revolution,” he said in the recorded message, as he called on Palestinians from east Jerusalem to northern Israel to join the fight and “expel the occupiers and demolish the walls.”

“We must set the earth on fire under the feet of the occupiers,” he said, claiming that Hamas had fired over 5,000 rockets into Israel.

Israeli Prime Minister Benjamin Netanyahu ’s office said he’d convene his security cabinet for urgent discussions.

The escalation comes at a delicate time for his far-right government, as protests against the government’s deeply divisive plan to overhaul the judiciary have spread even within the ranks of the military.

Hundreds of soldiers in the military reserves have either pulled out of training sessions or said they won’t report for duty over the judicial changes, threatening to undermine Netanyahu’s reputation as a security expert and raising fears about the effects on the operational readiness of Israel’s armed forces.

Salah Arouri, an exiled Hamas leader, said the operation was a response “to the crimes of the occupation.” He said fighters were defending the Al-Aqsa Mosque in Jerusalem and the thousands of Palestinian prisoners held by Israel.

The operation, coming on the major Jewish holiday of Simchat Torah, caught Israel off-guard, raising memories of the 1973 war in which Israel’s enemies launched a surprise attack on Yom Kippur.

The Israeli military confirmed Saturday that an infiltration had occurred in several locations near the Gaza border in southern Israel. It ordered residents to remain indoors.

“In the last hour, the Hamas terrorist organization had begun a massive shooting of rockets from the Gaza Strip into Israeli territory, and terrorists infiltrated into Israeli territory in a number of different locations,” it said.

Cities and towns in southern Israel emptied as the military closed roads near Gaza and millions of Israelis scrambled to bombs shelters while air raid sirens wailed overhead. In the kibbutz of Nahal Oz, just 4 kilometers (2.5 miles) from the Gaza Strip, terrified residents who were huddled indoors said they could hear constant gunfire echoing off the buildings.

The army said residents next to Gaza should stay in their homes due to the infiltration.

“With rockets we somehow feel safer, knowing that we have the Iron Dome (missile defense system) and our safe rooms. But knowing that terrorists are walking around communities is a different kind of fear,” said Mirjam Reijnen, a 42-year-old volunteer firefighter in Nahal Oz, adding that she and her three kids have been too scared to leave the shelter even for a moment to use the bathroom.

Israel has built a massive fence along the Gaza border meant to prevent infiltrations. It goes deep underground and is equipped with cameras, high-tech sensors and sensitive listening technology. The infiltration marked a major accomplishment — and escalation — by Hamas.

The sound of outgoing rockets whooshing through the air could be heard in Gaza and sirens wailed in Tel Aviv and Jerusalem during an early morning barrage that lasted for over two hours. Israel’s Magen David Adom rescue agency said a 70-year-old woman was critically injured when a rocket hit a building in southern Israel. Elsewhere, a 20-year-old man was moderately injured by rocket shrapnel, it said.

The launches came after weeks of heightened tensions along Israel’s volatile border with Gaza, and heavy fighting in the Israeli-occupied West Bank.

Israel has maintained a blockade over Gaza since Hamas, an Islamic militant group that opposes Israel, seized control of the territory in 2007. The bitter enemies have fought four wars since then. There have also been numerous rounds of smaller fighting between Israel and Hamas and other smaller militant groups based in Gaza.

The blockade, which restricts the movement of people and goods in and out of Gaza, has devastated the territory’s economy. Israel says the blockade is needed to keep militant groups from building up their arsenals. The Palestinians say the closure amounts to collective punishment.

The rocket fire comes during a period of heavy fighting in the West Bank, where nearly 200 Palestinians have been killed in Israeli military raids this year. Israel says the raids are aimed at militants, but stone-throwing protesters and people uninvolved in the violence have also been killed. Palestinian attacks on Israeli targets have killed over 30 people.

The tensions have also spread to Gaza, where Hamas-linked activists held violent demonstrations along the Israeli border in recent weeks. Those demonstrations were halted in late September after international mediation.

Adwan reported from Gaza City, Gaza Strip. AP writer Isabel DeBre contributed from Jerusalem.