BEIRUT >> The Israeli military said it struck Hezbollah’s headquarters in Beirut on Friday in a series of massive explosions that targeted the leader of the militant group and leveled multiple high-rise apartment buildings. The biggest blast to hit the Lebanese capital in the past year appeared likely to push the escalating conflict closer to full-fledged war. At least six people were killed and 91 were wounded, Lebanon’s health ministry said.

Hezbollah leader Hassan Nasrallah was the target of the strikes on the group’s headquarters, according to two people familiar with the matter who requested anonymity, including one U.S. official. The Israeli army declined to comment on who it was targeting. It was not immediately clear if Nasrallah was at the site, and Hezbollah did not comment on the report.

The death toll is likely to rise significantly as teams are still combing through the rubble of six buildings. Israel launched a series of strikes on other areas of the southern suburbs following the initial blast.

After the strikes, Prime Minister Benjamin Netanyahu abruptly cut short a visit to the United States to return home. Hours earlier, he addressed the U.N., vowing that Israel’s intensified campaign against Hezbollah over the past two weeks would continue — further dimming hopes for an internationally backed cease-fire.

Israeli army spokesman Rear Adm. Daniel Hagari said the strikes targeted the main Hezbollah headquarters, saying it was located underground beneath residential buildings.

The series of blasts at around nightfall reduced six apartment towers to rubble in Haret Hreik, a densely populated, predominantly Shiite district of Beirut’s Dahiyeh suburbs, according to Lebanon’s national news agency. A wall of billowing black and orange smoke rose into the sky as windows were rattled and houses shaken some 30 kilometers (18 miles) north of Beirut.

Footage showed rescue workers clambering over large slabs of concrete, surrounded by high piles of twisted metal and wreckage. Several craters were visible, one with a car toppled into it. A stream of residents carrying their belongings were seen fleeing along a main road out of the district.

Israel provided no immediate comment about the type of bomb or how many it used but the resulting explosion levelled an area greater than a city block. The Israeli army has in its arsenal 2,000 pound American-made “Bunker Buster” guided bombs designed specifically for hitting subterranean targets.

Richard Weir, crisis and weapons researcher with Human Rights Watch, said the blasts were consistent with that class of bomb.

Israel’s air forces followed with a new set of strikes early Saturday shortly after an Israeli military spokesman warned residents of three buildings to evacuate, saying they were being used by Hezbollah to hide weapons, including anti-ship missiles.

To a degree unseen in past conflicts, Israel this past week has aimed to eliminate Hezbollah’s senior leadership. But an attempt to assassinate Nasrallah – successful or not – would be a major escalation. The Pentagon said the U.S. had no advance warning of the strikes.

Nasrallah has been in hiding for years, very rarely appearing in public. He regularly gives speeches, but always by video from unknown locations. The site hit Friday evening had not been publicly known as Hezbollah’s main headquarters, though it is located in the group’s “security quarters,” a heavily guarded part of Haret Hreik where it has offices and runs several nearby hospitals.

Four hours after the strike, Hezbollah had still not issued any statement referring to it. Instead, it announced that it had launched a salvo of rockets at the Israeli city of Safed, which it said was “in defense of Lebanon and its people, and in response to the barbaric Israeli violation of cities, villages and civilians.” The Israeli military said a house and a car in Safed were hit, and officials said a 68-year-old woman suffered mild shrapnel wounds.

Israel dramatically intensified its airstrikes in Lebanon this week, saying it is determined to put an end to more than 11 months of Hezbollah fire into its territory. The escalated campaign has killed more than 720 people in Lebanon, including dozens of women and children, according to Health Ministry statistics. A predawn strike Friday in the mainly Sunni border town of Chebaa killed nine members of the same family, the state news agency said.

The White House said President Joe Biden was ordering his national security team to assess if further action is needed to beef up security for American interests in the Middle East.

Biden was briefed by national security aides several times on Friday following the strike on Hezbollah’s headquarters. The president, according to the White House, “has directed the Pentagon to assess and adjust as necessary U.S. force posture in the region to enhance deterrence, ensure force protection, and support the full range of U.S. objectives.”