(AFP) - UNICEF on Wednesday condemned a company selling breast milk from "vulnerable and poor" Cambodian mothers to Americans, hitting out at the commercialisation of nutrients needed by babies inside the kingdom.

The issue emerged this week after Cambodia said it had halted exports from Utah-based company Ambrosia Labs, which claims to be the first of its kind to bank human breast milk sourced overseas and export it into the United States.

The firm's customers are American mothers who want to supplement their babies' diets or cannot supply enough of their own milk.

The milk is pumped in Cambodia, frozen and shipped to the US where it is pasteurised and sold by the company for $20 each 5 oz (147 ml) pack -- roughly the volume of half a can of Coke.

Those donating their breast milk hailed from poor communities in Cambodia's capital Phnom Penh, where the scheme helped families top up meagre incomes.

On Monday Cambodia's customs department said it had stopped exports temporarily "because the product comes from a human organ" adding the government planned to hold talks on whether to let the trade continue.

UNICEF -- the arm of the UN protecting children -- said excess breast milk should remain in Cambodia, one of Southeast Asia's poorest countries, where many babies lack good nutrients.

"Breast milk banks should never be operated by exploiting vulnerable and poor women for profit and commercial purposes," Iman Morooka, the agency spokeswoman in Cambodia, told AFP.

"Breast milk could be considered as human tissue, the same as blood, and as such its commercialisation should be banned," she said.

Malnutrition "remains a threat to children's wellbeing in Cambodia, and proper breastfeeding is one of the key factors contributing to a child's good health and nutrition", she added.

Cambodian Health Minister Mam Bunheng declined to comment on the issue when contacted by AFP on Wednesday.

Ambrosia Labs did not respond to repeated requests for comment.

In previous press interviews the firm said its model encouraged Cambodian women to continue breast feeding, earned them much needed extra income and helped plug milk bank shortages in the US.

AFP visited the offices of Ambrosia Labs last week in Stung Meanchey, a poor suburb of Phnom Penh.

The office, which is labelled Khun Meada (mother's gratitude), was closed and women who sold their milk said they had been told operations were suspended.

Chea Sam, a 30-year-old mother, told AFP during an interview last week that she had been selling her breast milk for the last three months following the birth of her son.

She said she earned $7.5-$10 a day and she knew at least 20 other mothers doing the same.

In videos posted on the Facebook page of Khun Meada, several mothers appealed to the government to let them sell their milk to the company.

© Agence France-Presse