United Nations Secretary-General Antonio Guterres urged the warring sides in Yemen on Tuesday to reach a political settlement to end a four-year-old conflict that has left 22 million people in urgent need of aid.

“A negotiated political settlement through inclusive intra-Yemeni dialogue is the only solution. I urge all parties to engage with my new Special Envoy, Martin Griffiths, without delay,” Guterres told the one-day conference.

“All ports must remain open to humanitarian and commercial cargo, the medicines, food and the fuel needed to deliver them. Sanaa airport is also a lifeline that must be kept open,” he said.

Yemeni Foreign Minister Abdel-Malek al-Mekhlafi echoed the call for a return to the negotiating table and said that his internationally-recognised government was working to open ports and airports to humanitarian aid.

Mekhlafi said: “We need to find the ideal solution which is a return to the talks table, to put an end the war, to return to a sustainable system supported by the people of Yemen, including the putschist parties and those supported by the international community.”

The country’s unity and territorial integrity must be preserved, he added.

The U.N. conference,  is seeking pledges towards a $3 billion funding appeal to address the world’s worst humanitarian crisis.

The war has killed more than 10,000 people, displaced more than 2 million and driven the country .