PORT-AU-PRINCE – Haitian police detained 10 members of a US Christian group after they allegedly tried to leave the country with more than 30 children who survived the country's devastating earthquake.

News of the charges came as the UN's food agency prepared to launch a massive food effort targeted at vulnerable women in a bid to ease some of the chaos surrounding the relief effort.

Police had arrested five men and five women with US passports, as well as two Haitians, as they tried to cross into the neighboring Dominican Republic with 33 children late Friday, Haitian authorities said.

Border police "saw a bus with a lot of children. Thirty-three children. When asked about the children's documents, they had no documents," Haitian Culture and Communications Minister Marie Laurence Jocelyn Lassegue said.

The Americans were members of an Idaho-based charity called New Life Children's Refuge, said Social Affairs Minister Yves Christallin, adding: "This is an abduction, not an adoption."

The leader of the group, identified as Laura Silsby, said the group's aims were altruistic and that they were only seeking help for the children in the neighboring Dominican Republic, CNN reported.

"We are trusting the truth will be revealed, and we are praying for that," she said, adding that the matter was a misunderstanding over documentation.

But Patricia Vargas, head of an international center caring for the youngsters, said that officials at the Haitian Institute of Social Welfare, which deals with adoptions, told her "most of the kids have family."

Some of the older children had spoken to aid workers and "say their parents are alive, and some of them gave us an address and phone numbers," she said.

The US embassy confirmed that ten US citizens were being held for "alleged violations of Haitian laws related to immigration."

Workers from aid groups and other non-governmental and religious organizations have poured into Haiti in the aftermath of the January 12 quake which is believed to have killed some 170,000 people.

Amid fears that food is not reaching enough people, the World Food Program said it would open 16 fixed collection sites in Port-au-Prince on Sunday, aiming to feed two million people in two weeks.

Only female quake survivors will be allowed at the sites to avoid scenes at chaotic mobile handouts that have sometimes seen children and women muscled aside in the scramble for bags of rice, beans and cooking oil.

The aid effort suffered a further setback over the weekend, after the US military stopped flying injured Haitians to the United States for treatment because of a dispute over costs.

The governor of Florida has asked the US government to share the financial burden on his state's hospitals, putting a block on flights that have so far carried more than 500 people with spinal injuries, burns and other wounds.

The United States has spearheaded relief efforts since the 7.0-magnitude quake, which also injured around 200,000 and left more than one million homeless.

The aid effort has, however, drawn criticism for a lack of coordination.

Haitians, many of whom are living in squalid makeshift tent camps, have complained that relief has been slow to reach them on the ground.

Haitian Prime Minister Jean-Max Bellerive made a fresh appeal for 200,000 tents before the country's rainy season starts, most likely in May.

"We are very aware of the consequences to all of the people on the streets if it's starting to rain," Bellerive told CNN, adding that the government only had 3,500 tents so far.

Diseases such as diarrhea, measles, and tetanus are rising in tent camps, prompting UN agencies and the government to prepare a mass vaccination drive, while survivors also face rising insecurity with reports of rape and violence.

Aid officials have warned meanwhile that the reconstruction process in Haiti, already the poorest country in the Americas before the quake, will take decades.