The Saudi-led coalition had been named on the blacklist a year ago after the United Nations report blamed it for 60 percent of child deaths and injuries in Yemen in 2015 and half the attacks on schools and hospital.
"The Yemeni people's suffering has relentlessly intensified", he told the UN Security Council yesterday.
The United Nations has worked to avert attacks on Hodeidah port, where around 80 percent of Yemen's food imports arrive. The Houthi movement denies the allegations.
In March 2015, a Saudi-led coalition began a campaign in support of Hadi's government and against Houthi forces allied with ousted President Ali Abdullah Saleh. O'Brien said monthly air strikes in 2017 had tripled from a year ago, while monthly reports of armed clashes were up 50 percent.
"Death looms for Yemenis by air, land and sea", Special Envoy of the Secretary-General to Yemen, Ismail Ould Cheikh Ahmed told the 15-member Council in NY.
Every day spent without serious action means more destruction and death, he said, as well as the spread of terrorist groups - such as the Al Qaeda in the Arabian Peninsula - and "uncontrolled migration" through the Gulf of Aden to Yemen, where more than 41 migrants died in early August after being forced to abandon their boats and jump.
O'Brien and Ould Cheikh Ahmed also pushed the Saudi-led coalition to allow civilian traffic to land at the airport in Yemen's capital Sanaa. Since then, the Iranian-backed Houthis have been dislodged from most of the south, but remain in control of Sanaa and much of the north.
The conflict, which has been ongoing since 2014, is a "deplorable, avoidable, completely man-made catastrophe that is ravaging the country", O'Brien said.
"Today, millions of people in Yemen are facing a triple tragedy: the specter of starvation, the world's largest ever single-year cholera outbreak, and the daily deprivation and injustice of a brutal conflict that the world is allowing to drag on and on", said Stephen O'Brien, the under-secretary general for humanitarian affairs. "I call on all parties to a conflict, the security Council and the member States to take all measures possible to prevent the achievement of such violations", he adds.