The United Nations Children's Fund regional director says local Yemeni authorities are making it "impossible" for the delivery and distribution of much-needed humanitarian aid in Yemen and warned that impeding relief efforts could accelerate famine conditions.

Geert Cappelaere also told The Associated Press in an interview from Yemen that a U.S. call for a cease-fire is imperative to end the "brutal war."

Cappelaere, who visited the war-torn Red Sea port city of Hodeida and the capital Sanaa over the past two days as clashes and airstrikes intensified, said both Yemeni government and Houthi rebel authorities are being uncooperative.

"Respective authorities are not enabling us to do our work as fast as we should," he said.

Cappelaere said he can't bring the best nutrition experts to the country because of delays in granting visas and aid agencies are struggling to get supplies on time because of bureaucratic impediments.

He criticized authorities with "other interests" for creating delays in the arrival and distribution of supplies, without elaborating.

Most aid agencies operate in Houthi-held territories where militias impose restrictions on movement and force agencies to use their lists of beneficiaries.

Cappelaere's visit came shortly after the United States called for the cease-fire within 30 days. He said the situation in Yemen now to his last visit in 2017 is deteriorating, adding that "the war is taking hostage millions of Yemenis who can't afford basic needs."

Yemen has been at war since March 2015 when Houthis occupied northern Yemen, forcing the government into exile, resulting in a Saudi-led coalition being formed to support the government that has waged a destructive air campaign in the country.

Saudi Arabia, an ally of the US - which sells weapons worth billions of dollars and provides logistical support to the coalition - has come under heavy criticism for its conduct of the war that has left thousands dead and injured.

"An end to the conflict is ... a much-needed step but it needs to be complemented with investment and governance of this country that puts the interest of the people at the center and the interest of the children at the core of politics," Cappelaere said.

Three-quarters of Yemen's 29 million people are food insecure, 1.8 children suffer from malnutrition and 400,000 children under age 5 are in the worst stage of malnutrition - without intervention they might die. Every 10 minutes a child dies of preventable diseases.

"This is not an overstatement," Cappelaere said.

Around 40 percent of the 400,000 are located in Hodeida and its surroundings. Up to 5.5 million people might be added to the number of food insecure because of price hikes caused by the freefall in value of the local currency. Around 90 percent of Yemen's needs are imported from overseas.

While in Hodeida, the lifeline of the Houthi-controlled north, Cappelaere said he learned that families can't make it to the hospital because of constant fear of airstrikes and shelling or because they have no money to pay for transportation.

Yemeni forces under the command of the United Arab Emirates, a major pillar in the anti-Houthi coalition, are battling Houthis over control of the port and the coalition accuses Houthis of using the port to smuggle in weapons from Iran.

In his visit to Hodeida's main hospital, he saw cases of severe acute malnourished and children paralyzed by complications from diphtheria - an epidemic in Yemen.

"It's high time for authorities from both sides to take responsibility and enable that assistance without any conditions, without any hurdles," he said.