In the wake of renewed fighting in Yemen, the United States has called on all factions to work with the United Nations to broker a peaceful resolution to the over three-year conflict, the State Department said Monday."I have spoken with Emirati leaders and made clear our desire to address their security concerns while preserving the free flow of humanitarian aid and life-saving commercial imports," U.S. Secretary of State Mike Pompeo said in a statement."We expect all parties to honor their commitments to work with the U.N. Office of the Special Envoy of the Secretary-General for Yemen on this issue, support a political process to resolve this conflict, ensure humanitarian access to the Yemeni people, and map a stable political future for Yemen," the statement went on. Heavy fighting around Yemen's main port city of Hudaydah intensified over the weekend, even as the United Nations attempted to broker a cease-fire, according to military sources.Pompeo said the United States was closely monitoring the situation near Hudaydah — a lifeline for millions of Yemenis where most of the country's imports and aid supplies are handled.When asked about the situation, U.N. Secretary-General Antonio Guterres told reporters intense negotiations are taking place, with U.N. Special Envoy for Yemen Martin Griffiths shuttling between Sana'a, the U.A.E. and Saudi Arabia."There is a lull in the fighting to allow for them, and I hope that it will be possible to avoid a battle of Hudaydah," Guterres said Monday at the U.N.The U.N. estimates 22 million Yemenis are in need of some form of humanitarian assistance and protection, calling the conflict the world's worst humanitarian crisis. U.N. Coordinator Lise Grande warns cutting off imports through Hudaydah for any length of time will put Yemen's population at extreme, unjustifiable risk.Saudi Arabia began bombing Houthi rebels in support of the Yemeni government in March 2015. Since then, the U.N. estimates more than 10,000 people have been killed, most due to airstrikes.Last year, Yemen was gripped by the largest, fastest-spreading outbreak of cholera in modern history. The number of suspected cases of the disease topped 1 million and caused more than 2,000 deaths.Nike Ching, Margaret Besheer contributed to this report.