The United Nations has so far extended food assistance to 60,000 people in the capital of Haiti, which was struck by a catastrophic earthquake last week, with UN Secretary-General Ban Ki-moon expected to touch down in the capital Port-au-Prince on Sunday afternoon.

Within 24 hours of the Jan. 12 tremors, the UN World Food Program (WFP) had started distributing food and ultimately aims to reach 2 million people as part of its emergency program.

By Saturday night, it had fed at least 60,000 people impacted by the 7.0-magnitude earthquake, which is believed to have affected one third of Haiti's 9-million strong population, with ready-to-eat meals.

Given the security and logistical issues in transporting and delivering food in the capital, which was hit hardest by the tremors, WPF flew over Port-au-Prince on Saturday and Friday, as well as conducting on-the-ground inspections, to determine possible locations for food distributions, which require military escorts from the UN Stabilization Mission in Haiti (MINUSTAH).

"We are mobilizing all available resources to provide urgently needed food assistance as part of a swift and coordinated recovery effort," said WFP Executive Director Josette Sheeran.

Late on Saturday, the secretary-general announced with deep sadness that the top UN officials in Haiti perished in Tuesday's tremors.

In a statement issued by his spokesperson, Ban paid tribute to his special representative to Haiti, Hedi Annabi, as well as his Deputy Luiz Carlos da Costa and Acting Police Commissioner Doug Coates of the Royal Canadian Mounted Police.

"In every sense of the word, they gave their lives for peace," he said.

"Our hearts are with them, the families and friends of Hedi, Luiz, Doug and the many other UN heroes who gave their lives for Haiti and for the highest ideals of the United Nations," Ban said.

But "even weakened, MINUSTAH is operational," said Edmond Mulet, former UN special representative to Haiti and current assistant- secretary-general for peacekeeping operations, who was dispatched to the country to assume full command of the mission immediately after the quake struck.

Mulet, who is in charge of coordinating the massive aid effort, underscored the importance of collaboration between blue helmets and United States troops -- nearly 3,500 of whom will soon be deployed in Haiti -- to maximize efforts to provide relief.

The UN and its partners launched an appeal on Friday for 562 million U.S. dollars to help the victims of the earthquake, which has left basic services on the brink of collapse in Port-au-Prince. The UN estimates that 10 percent of the buildings in the city have been destroyed, leaving 300,000 people homeless, and many are fleeing the destruction.

The funds are intended to assist an estimated 3 million affected people over a period of six months, with half of the funds being earmarked for emergency food aid, with the rest targeted at health, water, sanitation, nutrition, early recovery, emergency education and other key needs.

The UN Office for the Coordination of Humanitarian Affairs ( OCHA) warned Saturday that unless fuel supplies are not replenished, humanitarian operations may be forced to shut down in the next few days.

Nearly 60 people have been pulled out of rubble alive by 27 search-and-rescue teams, comprising some 1,500 rescue workers and 115 dogs. So far, more than half of the worst-hit areas of Port-au- Prince have been covered.

OCHA said that the favorable climate and building structures have enhanced the chance of survival for those pinned by debris, indicating that the search-and-rescue phase can be prolonged.

The Office stressed that assistance priorities continue to also include medical services, shelter, food and water.

To keep families, friends and colleagues of UN personnel in Haiti up-to-date on the latest developments, the world body's peacekeeping and field support departments are utilizing the social networking sites Facebook and Twitter, with nearly 5,000 fans and almost 400 followers having been amassed so far, respectively.