The UN's World Food Programme (WFP) said the entire food system in Lebanon was reeling from the conflict, with Israel launching its heaviest strikes on the country this week.

Lebanon was drawn into the Middle East war on March 2 when Tehran-backed militant group Hezbollah began firing rockets into Israel to avenge the killing of Iranian supreme leader Ayatollah Ali Khamenei in US-Israeli airstrikes.

More than a million people have been displaced in Lebanon by the conflict, and Israel has launched a ground invasion in the south.

"What we're witnessing is not just a displacement crisis: it is rapidly becoming a food security crisis," said Allison Oman, the WFP's country director in Lebanon.

"We're already seeing clear signs of rising food prices across Lebanon. In just one month, the price of vegetables has surged by more than 20 percent, bread prices have increased by 17 percent.

"For families who are already struggling, this is deeply concerning."

Before March 2, around 900,000 people in Lebanon were facing food insecurity and WFP's latest analysis, expected next week, indicates that the number is set to rise, Oman said.

Speaking from Beirut, she described a worrying spiral of rising prices, increasing demand and disrupted incomes.

"There are supply chain disruptions and the whole food system has taken a blow," Oman told a press briefing in Geneva.

Farmers in southern Lebanon have not been able to work their fields, while rises in global fuel prices and difficulties accessing fertiliser are also having an impact.

Oman said 10 WFP convoys had gone out to reach populations in need in Lebanon since March 2, reaching 40,000 to 60,000 people, but several others had not been able to go because of security concerns.