Three months into the war, the United Nations warned that a "humanitarian catastrophe" was looming in Lebanon, with a quarter of its population needing aid.

"Communities across Lebanon have faced an appalling situation due to the escalation of hostilities," Imran Riza, the UN's resident humanitarian coordinator for Lebanon, told reporters in Geneva, speaking from Beirut.

He said Israeli attacks have killed more than 3,500 people and injured over 10,000 others since Hezbollah drew Lebanon into the wider Middle East war on March 2, firing rockets at Israel in retaliation for US-Israeli strikes that killed Iran's supreme leader.

"We have witnessed too many casualties, widespread and repeated displacement, destruction of housing and basic service infrastructure, and far-reaching psychological trauma," he said, calling for assistance to be scaled up.

"The toll on civilians is alarming and worsening by the day."

The UN had appealed for $308 million in March to support a massive emergency response led by Lebanon's government through to the end of May.

On Friday it said that another $331 million would be needed through the end of August.

"Repeated displacements, insufficient shelter capacity and limited prospects for safe return are deepening vulnerability," the appeal said, warning that "affected people are rapidly exhausting their coping capacities, and essential services are under increasing strain".

- 'Horrific' -

Only $185 million had so far been received out of the initial appeal, the UN humanitarian agency OCHA said, adding that that amount had helped provide assistance to around 680,000 people between March 2 and May 31.

The aim now, it said, was to more than double that number to reach all of the 1.4 million people in Lebanon -- around a quarter of the population -- estimated to need humanitarian assistance in the country.

Nearly one million people have fled their homes, including around 135,000 who are in collective shelters, while more than 1.2 million are facing acute food insecurity, Friday's appeal showed.

Price pressure was adding to the misery, with the cost of water, fuel and electricity up more than a third nationally, and as high as 70 percent in the conflict-affected areas, it said.

It also highlighted the strain that the conflict was placing on healthcare in Lebanon, with 62 hospitals and other health facilities either damaged or closed.

"Health workers and first responders are facing death and injury on a horrific scale," Riza said, also decrying how "entire neighbourhoods have been turned to rubble (and) families have lost their homes and livelihoods".

He said he had been "shocked by the devastation of infrastructure and essential services, hospitals and clinics hit by airstrikes", as well as the hundreds of schools that have been turned into displacement shelters.

- 'Humanitarian catastrophe' -

The United Nations Population Fund, the UN's sexual and reproductive health agency, meanwhile warned that women and girls were particularly vulnerable, and were increasingly facing a health and protection crisis.

Andrew Saberton, UNFPA's deputy head, pointed out that 16,000 pregnant women were among the displaced in the country.

"Around 1,800 women are expected to give birth every month, and yet healthcare facilities continue to come under attack," he told the Geneva press conference, speaking from Cairo.

Saberton said UNFPA was asking for $25 million, within the larger UN appeal, to reach 450,000 people by August, but had so far received just 16 percent of that amount.

"Sustained investment is essential to protect the health, safety, and dignity of women and girls and to prevent a deepening humanitarian catastrophe," he warned.