During their first conversation since a 7.0-magnitude trembler hit Haiti, Haitian President Rene Preval told United Nations Secretary-general Ban Ki- moon over the phone on Friday that the biggest problem his country faces is the lack of coordination among aid operations, according to the UN spokesperson's office. Preval said he intended to discuss problems of coordination with the acting head of the UN mission, Edmond Mulet, who arrived in Haiti Thursday afternoon. Mulet is replacing Hedi Annabi, who is still missing and believed to be under the rubble of the Christopher Hotel. In prior media reports, Prval said Annabi was dead. It is unclear whether Ban discussed Prval's comments or the fate of Annabi. Over the phone, Ban welcomed discussions between Mulet and Preval, and said that he had asked countries to coordinate their efforts with the UN, stressing the importance of cooperation with the United States. Ban informed Preval that he was working closely with former U.S. President and special envoy Bill Clinton and coordinating relief efforts with U.S. President Barack Obama. The United Nations has been scrambling to ramp up its humanitarian operations but with critical infrastructure damaged and the airport in Port-au-Prince running at full capacity, distribution of water, food and tents has been slow. Ban told Preval that the United Nations was 'fully mobilized' to bring assistance to the Haitian government and people. The UN family was doing all that it could, said Ban, and that the World Food Program (WFP) had started food distribution. Ban told reporters on Friday that the WFP is able to provide ready-made meals to 8,000 of the neediest people several times a day, a start he called 'a drop in the bucket.' In one month time, the WFP hopes to reach 2 million people. The secretary-general assured Prval that the United Nations ' is working for all the Haitian people' and 'expressed confidence that with patience, everyone would be able to work together to overcome this crisis.' 