The head of the World Health Organization (WHO) and other UN staff were at Yemen's international airport in Sanaa on Thursday during Israeli air strikes which are reported to have killed at least six people,
BBC reports.
WHO Director General Tedros Adhanom Ghebreyesus said they were about to board a plane when the attacks began.
Houthi-run Saba news agency said three people were killed at the airport and 30 injured. It said another three people were killed and 10 wounded in the western Hodeidah province.
The Iran-backed rebel group described the attacks - which also hit power stations and ports - as "barbaric". Israel's military said it carried out "intelligence-based strikes on military targets".
It is unclear whether the fatalities were civilians or Houthi rebels.
In a statement on X, Dr Tedros said he was in Yemen "to negotiate the release of UN staff detainees and to assess the health and humanitarian situation" in the country. He provided no further details about who the UN detainees were.
Referring to the strikes on Sanaa's airport, he said: "The air traffic control tower, the departure lounge - just a few meters from where we were - and the runway were damaged.
"We will need to wait for the damage to the airport to be repaired before we can leave," Dr Tedros added.
UN Secretary General António Guterres called the strikes "especially alarming".
"I regret the recent escalation between Yemen and Israel, and remain deeply concerned about the risk of further escalation in the region." he wrote on X.
In a statement, the Israel Defense Forces (IDF) said its "fighter jets conducted intelligence-based strikes on military targets belonging to the Houthi terrorist regime on the western coast and inland Yemen".
It targeted "military infrastructure" at Sanaa's airport as well as the Hezyaz and Ras Kanatib power stations, and sites in the Al-Hudaydah, Salif and Ras Kanatib ports on the west coast, the IDF said.
In comments shortly after the strikes, Israel's Prime Minister Benjamin Netanyahu said it would "continue to cut off the terror arm of the Iranian axis of evil until we complete the job", adding "we are only just starting with [the Houthis]".
Early on Friday, the IDF reported that one missile fired from Yemen was intercepted before crossing into Israeli territory.
Mohammed Ali al-Houthi, head of the Houthis' supreme revolutionary committee, called Thursday's strikes on Yemen "barbaric" and "aggressive".
He said that "confrontations with American and Israeli arrogance" will continue until the conflict in Gaza stops.
Several people injured by the strikes at the airport in Sanaa told Houthi-run broadcaster Al Masirah that the runway was struck three times before the airport's control tower was also hit.
