Planes from a Saudi-led coalition struck Yemeni provinces near the Saudi border overnight, killing at least 43 civilians, Houthi sources said, as 22 aid agencies warned that fuel shortages could halt their work.

The strikes occurred after Yemen’s Houthi fighters fired mortar bombs and rockets at a Saudi Arabian border town on Tuesday for the first time since the coalition began a military campaign against them on March 26.

The conflict has disrupted imports in Yemen, where about 20 million people or 80 percent of the population are estimated to be going hungry, a statement by the United Nations and the Yemen International NGO Forum said.

A shortage of fuel has crippled hospitals and food supplies in the past few weeks, and the U.N.’s World Food Programme has said its monthly fuel needs have leapt from 40,000 litres a month to 1 million litres.

“Millions of lives are at risk, in particular children, and soon we will not be able to respond,” Edward Santiago, country director for Save the Children, said in the statement.

France24