Hamas blames Israel for the death of a senior official in Lebanon.

Israel and the surrounding region were on edge Wednesday, a day after the assassination of a top Hamas leader in Lebanon heightened worries that the war in Gaza could spill over into a broader conflict.

Hamas blamed Israel for the death of Saleh al-Arouri, the senior-most official of the group to be killed since the Oct. 7 attacks in Israel. Officials with the Israeli military would not comment on whether their forces were behind the explosion that killed him in a suburb of Beirut. Lebanese and U.S. officials also ascribed the attack to Israel.

Mr. al-Arouri was killed in the heart of a neighborhood with the offices of Hezbollah, the powerful Lebanese militant group and Hamas ally, likely putting pressure on the group to strike back. Hezbollah’s leader, Hassan Nasrallah, has warned that any assassinations in Lebanon would elicit a strong response.

Rear Adm. Daniel Hagari, the Israeli military’s chief spokesman, said in a televised briefing that Israeli forces were “on very high alert on all fronts, for defensive and offensive actions.” He emphasized that Israel was “focused on fighting Hamas,” in what some Israeli analysts interpreted as a suggestion that it did not seek a wider war with Hezbollah.

Lebanon’s state news agency reported that an “enemy raid” had struck the Hamas office in Beirut’s southern suburbs, killing seven people, including Mr. al-Arouri. Ismail Haniyeh, Hamas’s top political leader, said the strike had killed Mr. al-Arouri, two Hamas military commanders and four other members.

Najib Mikati, Lebanon’s caretaker prime minister, in blaming Israel for the attack, condemned what he said was an attempt to drag Lebanon into “a new phase” of the conflict.

Iran also condemned the assassination. Nasser Kanaani, a spokesman for Iran’s Foreign Ministry, said the killing was a result of Israel’s “desperate and heavy defeat” during the Oct. 7 assault and the “heroic defiance” of Hamas fighters since. After Mr. al-Arouri’s death was announced, the Iranian news media published photos of Mr. al-Arouri meeting Iran’s supreme leader, Ayatollah Ali Khamenei.

Mr. al-Arouri had worked with Yahya Sinwar, Hamas’s chief in Gaza, in recent years to link the group’s military wing more closely to Iran, which, regional security officials say, probably helped the group develop some of the capabilities it used in the Oct. 7 attack. Israel has accused Mr. Sinwar of helping to plot the assault, which officials say killed about 1,200 people and saw 240 others abducted to Gaza.