An Israeli strike on a mosque in the Gaza Strip early Sunday killed at least 19 people, Palestinian officials said, as Israel intensified its bombardment of northern Gaza and southern Beirut in its widening war on Iran-allied militant groups across the region.

Israel is still battling Hamas in Gaza nearly a year after its Oct 7 attack, and has opened a new front against Hezbollah in Lebanon, which has been trading fire with Israel along the border since the war in Gaza began. Israel has also vowed to strike Iran itself after it launched a ballistic missile attack on the country last week.

The widening conflict risks drawing in the United States, which has provided crucial military and diplomatic support to Israel, as well as US-allied Arab countries that host American forces. Iran-allied militant groups in Syria, Iraq and Yemen have also joined in with long-distance strikes on Israel.

Strikes across Gaza and new evacuation orders

The strike in Gaza hit a mosque where displaced people were sheltering near the main hospital in the central town of Deir al-Balah. Israel said it targeted a Hamas command and control center embedded among civilians, without providing evidence.

An Associated Press journalist counted the bodies at the Al-Aqsa Martyrs Hospital morgue. Hospital records showed that the dead were all men, while another man was wounded.

The military meanwhile announced a new air and ground offensive in Jabaliya, in northern Gaza, home to a densely populated refugee camp dating back to the 1948 war surrounding Israel's creation. It circulated photos and video footage showing a column of tanks heading toward the area.

The military said its forces had encircled Jabaliya as warplanes struck militant sides ahead of their advance. Over the course of the war, Israel has carried out several large operations there, only to see militants regroup.

Israel also ordered new evacuations in northern Gaza, which largely emptied out in the early weeks of the war when Israel ordered its entire population to flee south. Up to 300,000 people are estimated to have remained there despite harsh conditions and heavy destruction.

“We are in a new phase of the war,” the military said in leaflets dropped over the area. “These areas are considered dangerous combat zones.”

Avichay Adraee, a spokesman for the Israeli military, said it has expanded the so-called humanitarian zone in southern Gaza, urging people to head there. The zone includes sprawling tent camps where hundreds of thousands of people have already sought refuge, and Israel has carried out strikes inside it against what it says are fighters sheltering among civilians.

Palestinian residents reported heavy Israeli strikes across northern Gaza. The Civil Defense, first responders who operate under the Hamas-run government, said several homes and buildings had been hit and they were not able to reach them because of the bombardment.

Many posted about the airstrikes and mourned their relatives on social media. Imad Alarabid said in a Facebook post that an airstrike on his home in Jabaliya killed a dozen of his family members, including his parents.

Local journalists said one of their colleagues, Hassan Hamd, was killed in artillery shelling on his home in Jabaliya. He had worked as a freelance TV reporter and his footage had aired on Al Jazeera and other networks. Anas al-Sharif, an Al Jazeera reporter in northern Gaza, confirmed his death.

The latest strikes add to the mounting Palestinian death toll in Gaza, which is nearing 42,000, according to the Palestinian Health Ministry. The ministry does not differentiate between civilian and militant deaths, but many of the dead were women and children.

Hamas-led militants killed some 1,200 people in the Oct. 7 attack and took another 250 hostage. They are still holding around 100 captives, a third of whom are believed to be dead.

Heavy bombardment of southern Beirut

In Beirut, airstrikes lit up the skyline and loud explosions echoed across the southern suburbs, known as the Dahiyeh, throughout the night, as Israel struck what it said were Hezbollah militants sites. The strikes reportedly targeted a building near a road leading to Lebanon's only international airport and another formerly used by the Hezbollah-run broadcaster Al-Manar.

Israel's military confirmed it was striking targets near Beirut and said about 30 projectiles had crossed from Lebanon into Israeli territory, with some intercepted.

Hezbollah said it successfully targeted a group of Israeli soldiers in northern Israel “with a large rocket salvo, hitting them accurately.” It was not possible to confirm the claim.

At least 1,400 Lebanese, including civilians, medics and Hezbollah fighters, have been killed and 1.2 million driven from their homes in less than two weeks. Israel says it aims to drive the militant group away from its border so that tens of thousands of Israeli citizens can return to their homes.

Iranian-backed Hezbollah, the strongest armed force in Lebanon, began firing rockets into Israel almost immediately after Hamas' Oct. 7 attack, calling it a show of support for the Palestinians. Hezbollah and Israel's military have traded fire almost daily.

Last week, Israel launched what it said was a limited ground operation into southern Lebanon after a series of attacks killed longtime Hezbollah leader Hassan Nasrallah and most of his top command. The fighting is the worst since Israel and Hezbollah fought a monthlong war in 2006. Nine Israeli soldiers have been killed in ground clashes that Israel says have killed 440 Hezbollah fighters.

It is not possible to verify battlefield reports from either side.

Iran's foreign minister, Abbas Araghchi, told reporters in Damascus that “we are trying to reach a cease-fire in Gaza and in Lebanon.” The minister said Middle Eastern and other countries had put forward initiatives, without elaborating.

Araghchi spoke a day after the supreme leader of Iran praised its recent missile strikes on Israel and said it was ready to do it again if necessary.

On Saturday evening, Israeli Prime Minister Benjamin Netanyahu said “Israel has the duty and the right to defend itself and respond to these attacks, and it will do so.” On Lebanon, he said ”we are not done yet.”