The United Nations signed an agreement with the United States in Haiti clarifying humanitarian duties and responsibilities in what was considered by many a murky partnership, a senior UN official said on Friday from Haiti's capital.

"The Americans will be dedicated to the distribution of humanitarian aid and providing security to that distribution," said acting chief of the UN Mission in Haiti Edmond Mulet via video link, while the UN Mission in Haiti will continue to perform its "traditional role" in assisting the Haitian National Police and guaranteeing security and stability.

Over the past week, the U.S. has come under fire for its beefed up military presence on the Caribbean island. The U.S. military, which took control of Haiti's airport after the earthquake hit on Jan. 12, reportedly turned away cargo planes carrying humanitarian aid from the World Food Program and France.

General Douglas Fraser, who is in charge of the U.S. Southern Command, announced on Thursday that nearly 20,000 U.S. troops are expected to operate on and offshore, by Sunday. And Washington has said it plans to stay in the country for the long term.

"We are there for the long term, this is not something that will be resolved quickly and easily," U.S. Deputy Ambassador to the UN Alejandro Wolff said here on Thursday.

Several counties have deplored the large number of U.S. troops, including Nicaraguan President Daniel Ortega, who said Haiti seeks "humanitarian aid, not troops."

On Wednesday, Bolivian President Evo Morales said the U.S. should not use "a natural disaster to militarily occupy Haiti," and went so far as to say that "Haiti does not need more blood."

His comments were echoed again here on Friday during a meeting of the General Assembly, in which the world's countries adopted a resolution calling on the international community to provide Haiti with speedy and sustainable support.

Bolivia's deputy envoy to the UN, Pablo Solon-Romero said the world needs to overcome neocolonialism, which is the cause of Haiti's poverty in the first place.