The United Nations appealed on Wednesday for $2.1 billion to provide food and other life-saving assistance to 12 million people in Yemen who face the threat of famine after two years of war.

"The situation in Yemen is catastrophic and rapidly deteriorating," Jamie McGoldrick, U.N. humanitarian coordinator in Yemen, said in the appeal document.

"Nearly 3.3 million people - including 2.1 million children - are acutely malnourished."

Yemen has been divided by nearly two years of civil war that pits the Iran-allied Houthi group against a Sunni Arab coalition led by Saudi Arabia. At least 10,000 people have been killed in the fighting, which has unleashed a humanitarian crisis in the desperately poor Arabian Peninsula country.

In all, nearly 19 million Yemenis - more than two-thirds of the population - need assistance and protection, the U.N. said.

"Ongoing air strikes and fighting continue to inflict heavy casualties, damage public and private infrastructure, and impede delivery of humanitarian assistance," it said.

"The Yemeni economy is being wilfully destroyed," it added, saying that ports, roads, bridges, factories and markets have been hit.

An estimated 63,000 Yemeni children died last year of preventable causes often linked to malnutrition, the U.N. Children's Fund (UNICEF) said last week.

“In Yemen, if bombs don’t kill you, a slow and painful death by starvation is now an increasing threat,” Jan Egeland, secretary-general of the Norwegian Refugee Council, said in a separate statement as the U.N. plan was launched.

A military coalition led by Saudi Arabia entered Yemen's civil war in March 2015 to try to reinstate President Abd-Rabbu Mansour Hadi after he was ousted from the capital Sanaa by the tribal Houthis, who are fighting in an alliance with troops loyal to former President Ali Abdullah Saleh.

The United States has sent the Navy destroyer USS Cole to patrol off Yemen's coast to protect waterways from Houthi militia aligned with Iran, U.S. officials last week, amid rising tension between Washington and Tehran.

Oxfam accused Britain and other powers backing the Saudi-led coalition of "political complicity" in the Yemen conflict.

"The UK Government's calculated complicity risks accelerating Yemen toward a famine, putting millions of lives at risk and making a mockery of their global obligations to those in peril," Mark Goldring, chief executive of Oxfam GB, said in a statement.