FILE - In this Aug. 25, 2017 file photo, boys stand on the rubble of a house destroyed by Saudi-led airstrikes in Sanaa, Yemen. The Saudi-led coalition fighting in Yemen is blaming a rebel missile launch on Iran and warning it could be "considered as an act of war." Early Monday, Nov. 6, 2017, the coalition also closed off the land, sea and air ports to the Arab world's poorest country over the missile launch targeting Riyadh. (AP Photo/Hani Mohammed, File)

The U.N. humanitarian chief warned Wednesday that unless the Saudi-led military coalition lifts its blockade on Yemen the war-torn nation will face "the largest famine the world has seen for many decades, with millions of victims."

Mark Lowcock told reporters after briefing the U.N. Security Council behind closed doors that there must be an immediate resumption of regular air flights to the cities of Aden and Sanaa by the United Nations and its humanitarian partners. He said there also has to be immediate access to all ports, especially for food, fuel, medicine and other essential supplies.

The coalition tightened its blockade in Yemen this week after a ballistic missile fired by Houthi rebels was intercepted near the Saudi capital — an act condemned by Lowcock and the Security Council.

The U.N. said aid agencies were given no prior notice of the Saudi decision to shut down all land, air and seaports in Yemen.

Lowcock said he told the council that "there will be famine in Yemen" unless five steps are taken immediately.

"It will not be like the famine that we saw in South Sudan earlier in the year where tens of thousands of people were affected," he said. "It will not be like the famine which cost 250,000 people their lives in Somalia in 2011. It will be the largest famine the world has seen for many decades, with millions of victims."

He said the five immediate steps are:

—Resumption of air services.

—Assurances flights will not be disrupted.

—Opening of all ports to humanitarian and commercial vessels, especially those with critical supplies.

—Agreement to keep a U.N. World Food Program ship in waters off Aden.

—Halt to interference with all vessels that have passed inspection by the U.N. Verification and Inspection Mechanism "so that they can proceed to port as rapidly as possible."

Lowcock stressed the last point saying, "This is important because humanitarian access to the ports was inadequate even before the measures announced on Nov. 6" by the coalition.

"What we need to see is a reduction of blockages on all sides, not an increase on them," he said.

David Beasley, executive director of the World Food Program, told AP on Monday that out of Yemen's population of 27 million to 28 million people, 19 million to 20 million "do not know where they're going to get their next meal."

The agency is reaching only 7 million Yemenis, he said, "partly because of lack of funds and partly because of lack of access" by the coalition and the Houthis.

Lowcock said he couldn't put a timeline on famine if the Saudi blockade isn't lifted, but it is inevitable.

"Children are losing their lives all the time in Yemen," he said, because they are malnourished and don't have the ability to fight off even a cold.

The Security Council expressed concern about "the dire humanitarian situation in Yemen, with 6.8 million people threatened with famine and suspected cholera cases at over 900,000."

The council emphasized the importance of keeping all of Yemen's ports and airports functioning "as a critical lifeline for humanitarian support and other essential supplies."

Council members reiterated the need for the coalition and the Houthis "to provide full, safe, rapid and unhindered access for humanitarian supplies and U.N. personnel to the population of all affected governorates, including by air, land and sea."

News from © The Associated Press, 2017