BEIRUT/JERUSALEM - Israel's military said it killed 15 Hezbollah militants in southern Lebanon on Thursday and bombed Beirut after its forces suffered their deadliest day on the Lebanese front in a year of clashes with the group.

Israel, which has been fighting with Hamas in Gaza for almost a year, sent its troops into southern Lebanon after two weeks of intense airstrikes, in an escalating conflict that risks drawing in the United States and Iran.

On Thursday, Israel's military said it had "eliminated" Rawhi Mushtaha, the head of the Hamas government in Gaza, along with senior security officials Sameh al-Siraj and Sami Oudeh in strikes three months ago.

In Lebanon, an airstrike on the municipality building of the southern Lebanese town of Bint Jbeil killed 15 Hezbollah members, Israel said.

READ MORE: Israeli troops 'infiltrate southern Lebanese villages'

Lebanon's health ministry said the death toll in the Beirut strike had climbed to nine and the civil defense group Islamic Health Authority said seven of its staff including two medics had been killed.

Reuters witnesses reported hearing a massive blast, which a security source said had targeted a building in the district of Bachoura a few hundred meters from parliament, the closest an Israeli strike has come to the central downtown district of Beirut.

Israel said it had conducted a precise air strike on the Lebanese capital.

"Another sleepless night in Beirut. Counting the blasts shaking the city. No warning sirens. Not knowing what’s next. Only that uncertainty lies ahead. Anxiety and fear are omnipresent," UN special coordinator in Lebanon, Jeanine Hennis-Plasschaert, said on X on Thursday.

READ MORE: Diversions, disruptions: Aviation grapples with Middle East escalation

Israel said on Wednesday eight soldiers were killed in ground combat in south Lebanon as its forces thrust into its northern neighbor.

Iran launched its largest-ever assault on Israel on Tuesday in what it said was retaliation for Israel's assassination of senior Hamas and Hezbollah leaders and its operations in Gaza and Lebanon.

Tehran said its attack was over, barring further provocation, but Israel and the United States have promised to hit back hard.

Qatar's Emir Sheikh Tamim bin Hamad Al-Thani called for serious ceasefire efforts to stop Israel's "aggression" in Lebanon and said no peace was possible in the Middle East without the creation of a Palestinian state.

What is happening in the Middle East is a "collective genocide", he said at the Asia Cooperation Dialogue summit in Doha, adding that his country has always warned of Israel's "impunity".

Speaking at the same gathering, Iranian President Masoud Pezeshkian warned against "silence" in the face of Israel's "warmongering".

"Any type of military attack, terrorist act or crossing our red lines will be met with a decisive response by our armed forces."

ALSO READ: Iran says deterrence established to counter potential Israeli attack on nuke sites

More than a dozen Israeli missiles also hit the southern suburb of Dahiyeh, where Hezbollah leader Hassan Nasrallah was killed last week, and loud blasts were heard, Lebanese security officials said.

Houthis target Tel Aviv

The Lebanese border front opened after Hezbollah fired missiles at Israel on Oct 8 in support of Hamas.

Since then Israel has assassinated many Hamas and Hezbollah leaders and commanders.

The elimination of Nasrallah dealt a major blow to Hezbollah. Under his leadership, the group developed into Lebanon's most influential military and political force with a wide reach in the Middle East.

Yemen's Houthis and armed groups in Iraq have also launched attacks in the region in support of Hamas in the war in Gaza.

The Houthis, who have been firing missiles, sending armed drones and launching boats laden with explosives at commercial ships with ties to Israeli, US and UK entities since last year, said they launched a successful attack on Israel's commercial capital Tel Aviv with drones.

Israel said it intercepted a suspicious aerial target in the area of central Israel early on Thursday.

The Israel Defense Forces (IDF) urged residents of Lebanese villages who have evacuated their homes not to return until further notice.

ALSO READ: Deaths surge as Israel launches more raids in south Lebanon

"IDF raids are continuing," spokesperson Avichay Adraee said on X on Thursday.

More than 1,900 people have been killed and over 9,000 wounded in Lebanon in almost a year of cross-border fighting, with most of the deaths occurring in the past two weeks, according to Lebanese government statistics.

Caretaker Prime Minister Najib Mikati said about 1.2 million Lebanese had been displaced by Israeli attacks.

Nightclub becomes displaced shelter

More than 300 of those displaced have taken shelter in a Beirut nightclub, once known for hosting glitzy parties and where staff are now using their guest-list clipboards to register residents.

"We're trying to keep strong," said Gaelle Irani, who was formally in charge of guest relations, taking a brief break from finding people a corner to live in.

"It's just overwhelming. So overwhelming and sad. But just as this was a place for people to come enjoy themselves, it's now a place to shelter people and we are doing everything we can to help and be there for them."

Hassan Shaaban, a fisherman from Sidon, said he has been struggling to make a living as the fighting rages.

READ MORE: Israel military starts ‘limited’ ground campaign in Lebanon

"What can we do, we need to be able to live, we are working while they are striking, yesterday night was very intense," he said.

The Israeli military said regular infantry and armored units joined ground operations in Lebanon on Wednesday as Iran's missile attack and Israel's promise of retaliation fanned concern of a wider conflict in the oil-producing Middle East.

Israel's addition of infantry and armored troops from the 36th Division, including the Golani Brigade, the 188th Armoured Brigade and the 6th Infantry Brigade, indicated that the operation is expanding beyond limited commando raids.

READ MORE: Hezbollah deputy head vows to continue defending Lebanon

Western nations have drafted contingency plans to evacuate citizens from Lebanon after Tuesday's dramatic escalation, but none have launched a large-scale military evacuation yet, though some are chartering aircraft as Beirut airport stays open.