An Israeli airstrike on the municipal building in Nabatieh, a major town in southern Lebanon, which serves as a provincial capital, killed at least six people including the mayor, two security sources said.

Hours earlier, at least one Israeli strike hit Beirut's southern suburbs, Reuters witnesses said.

Reuters witnesses heard two blasts and saw plumes of smoke emerging from two separate neighbourhoods. It came after Israel issued an evacuation order early on Wednesday, which mentioned only one building.

Huwaida Turk, the governor of Nabatiyeh province, told The Associated Press that Mayor Ahmad Kahil was among those killed.

The Israeli military has in recent weeks carried out strikes on Beirut's southern suburbs, the stronghold of Iran-backed Hezbollah, without advance warnings, or with a warning for one area while striking more broadly.

The Israeli military said it conducted a strike on an underground Hezbollah weapons stockpile in the southern Beirut suburb of Dahiyeh.

"Prior to the strike, numerous steps were taken to mitigate the risk of harming civilians, including advancing warnings to the population in the area," the Israeli military said.

And in Qana, Lebanon's Civil Defence said 15 bodies had been recovered from the rubble of a building from an airstrike and that rescue efforts were still underway. There was no immediate comment from the Israeli military on the strikes late Tuesday.

Israeli military evacuation orders now affect more than a quarter of Lebanon, according to the UN refugee agency, two weeks after Israel began incursions into the south of the country that it says are aimed at driving back Hezbollah.

U.S., EU express separate war concerns

Some Western countries have been pushing for a ceasefire between the two neighbours, as well as in Gaza, though the United States says it continues to support Israel and was sending an anti-missile system and troops.

On Tuesday, State Department spokesperson Matthew Miller said the U.S. had expressed its concerns to Prime Minister Benjamin Netanyahu's administration on the recent strikes.

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"When it comes to the scope and nature of the bombing campaign that we saw in Beirut over the past few weeks, it's something that we made clear to the government of Israel we had concerns with and we were opposed to," he told reporters, adopting a harsher tone than Washington has taken so far.

Israel has also come under scrutiny because of its dealings with the UN peacekeeping force UNIFIL in south Lebanon. Since an Israeli ground operation against Hezbollah militants began on Oct. 1, UNIFIL positions have come under fire and two Israeli tanks burst through the gates of one of its bases, the UN says. Five peacekeepers have been injured.

European Union countries that contribute have no intention of pulling back despite Israeli calls to do so, Austrian Foreign Minister Alexander Schallenberg said.

Sixteen EU countries, including Austria, contribute to UNIFIL and the recent incidents have sparked widespread alarm among European governments.

The last time Beirut was hit was on Oct. 10, when two strikes near the city centre killed 22 people and brought down entire buildings in a densely populated neighbourhood.

Over 1 million displaced

The Middle East, meanwhile, has been on edge since Iran attacked Israel with a barrage of missiles on Oct. 1 after a similar large-scale operation in April. Israel has promised to retaliate.

Iran's allies in its "Axis of Resistance" to Israeli and U.S. interests — Lebanon's Hezbollah, Yemen's Houthis and armed groups in Iraq — have staged attacks in the region in support of Hamas in the Gaza war, complicating efforts to ease tensions.

Israel has been turning up the heat on Hezbollah since it began incursions into Lebanon after killing Hezbollah leaders and commanders, including its veteran secretary-general Hassan Nasrallah last month in the biggest blow to the group in decades.

With diplomatic efforts stalled, the fighting continues.

Israeli strikes in Lebanon have killed at least 2,350 people over the last year and left nearly 11,000 wounded, according to the health ministry, and more than 1.2 million people have been displaced.

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The toll does not distinguish between civilians and combatants but includes hundreds of women and children.

Around 50 Israelis, both soldiers and civilians, have been killed in the same period, according to Israel.

The figures underscore the heavy price Lebanese are paying as Israel tries to destroy Hezbollah's infrastructure in their conflict, which resumed a year ago when it began firing rockets at Israel in support of Hamas at the start of the Gaza war.