The Houthis, who drove the government into exile in 2014, control much of north Yemen, including the capital Sanaa.
On Friday, it conducted airstrikes on Sana, the Houthi-occupied capital.
Secretary of State Mike Pompeo on Tuesday urged a cease-fire, specifically citing missile and drone strikes into Saudi Arabia and the United Arab Emirates from Houthi-controlled areas of Yemen.
Geert Cappelaere also told The Associated Press in an interview from Yemen that a USA call for a cease-fire is imperative to end the "brutal war".
Pompeo also said the USA was also embarking on a new push for peace in Yemen, where as many as 50,000 have died and the country has been plunged into a major humanitarian crisis.
Cappelaere said he can't bring the best nutrition experts to the country because of delays in granting visas and that aid agencies face bureaucratic impediments the delay the import of supplies.
"We have evidence that today in Yemen every 10 minutes a child under the age of five is dying from preventable diseases and severe acute malnutrition", he said.
Most aid agencies operate in Houthi-held areas where they face movement restrictions.
The airstrikes in Sanaa came days after a USA call for an urgent halt to the Saudi-Iran proxy war in Yemen and the start of negotiations in November toward a political settlement of the conflict.
Concerned by the rise of the Houthis, believed to be backed by Iran, a US-backed Saudi-UAE military coalition launched an intervention in 2015 in the form of a massive air campaign aimed at reinstalling Hadi's government. 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 40 per cent of the 400,000 are located in and around Hodeida, which has been the target of a stalled coalition offensive in recent months. Residents in Sanaa reported dozens of airstrikes overnight in and around the airport that made the whole city quake. The killing prompted critics to urge an end to American arms sales to the kingdom and a reappraisal of US military support for the Saudi-led Arab coalition that has been bombing Iranian-supported Houthi rebels, sometimes at the expense of killing civilians.
"It's high time for authorities from both sides to take responsibility and enable that assistance without any conditions, without any hurdles", he said.