The U.N. envoy to Yemen says the redeployment of rival factions in the key port city of Hodeida is "slow" but will happen.

Hodeida has been the focus of months of U.N.-brokered talks with the government.

Martin Griffiths told the Associated Press on Thursday that the Hodeida cease-fire agreed on in December in Sweden by the rival parties is holding. But he warns the alternative would lead to "unthinkable" humanitarian disasters.

Hodeida is the main entry point for aid to Yemen, where nearly four years of war has spawned the world's worst humanitarian crisis.

The war in Yemen started in 2014 when Houthi rebels swept the northern part of the country and forced the internationally recognized government to flee the country before seeking military intervention by the Saudi-led coalition.