He stressed the keenness of the joint forces to adopt and implement the rules of engagement, in accordance with the rules and provisions of worldwide humanitarian law, the most important of which was "the assumption that every person in Yemen is a civilian until proven otherwise".
Samad held the post of president in the Houthi-backed political body which runs most of northern Yemen.
Health ministry spokesman Abdel-Hakim al-Kahlan said ambulances were initially unable to reach the site of the bombing for fear of subsequent airstrikes as the jets continued to fly overhead.
Meanwhile, at least 20 civilians were killed after Saudi Arabian airstrikes hit a wedding party in northern Yemen.
It was the third deadly attack on civilians in recent days.
The war devastating Yemen is now in its fourth year, with human rights organisations repeatedly accusing the Saudi-led coalition of targeting civilian areas.
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"The Secretary-General reminds all parties of their obligations under worldwide humanitarian law concerning the protection of civilians and civilian infrastructure during armed conflicts." a United Nations statement said.
Guterres also called for a transparent investigation.
The warplanes twice hit the wedding ceremony.
However, one must take note that the only media sources reporting the tanker seizure are Saudi sources and there has been no confirmation from an external source that the Houthis have actually seized any takers yet. On April 3rd, a Saudi oil tanker was attacked by Houthi militias in worldwide waters west of Hodeidah port which is under the control of armed militias. We'll have more on the latest attack and the crisis in Yemen after headlines.
Also on Monday, the coalition said it shot down two new ballistic missiles fired by the Houthis, who claimed to target facilities belonging to the kingdom's oil giant Aramco in southern Jizan city.
Since November, the militia has launched several ballistic missiles at Saudi Arabia, all of which have been intercepted by anti-aircraft defences.