From the introduction to the Final Report of the UN Panel of Experts on Yemen, 26th January 2018:
“Following the missile attack on Riyadh on 4 November 2017, the Saudi Arabia-led coalition ordered the closure of all land crossings into, and all seaports and airports in Yemen. Entry points under the control of the government of Yemen were quickly re-opened, while those under the control of the Houthis, such as Hudaydah, remained closed for weeks. This had the effect of using the threat of starvation as an instrument of war.”
Full report: https://reliefweb.int/sites/reliefweb.int/files/resources/N1800513.pdf
Stop Starving Yemen 