When asked about her engagement party this summer, little Sunam glanced blankly at her family, then fiddled with her gold-sequined engagement outfit - a speechless response not out of shyness, but because she does not yet talk much. Sunam is 3.

The toddler was engaged to her 7-year-old cousin Nieem in June, in a match made by their parents.

Despite the efforts of the government and rights groups, the engagement and marriage of children still persists in this country, especially among poor, uneducated families or in the countryside.

About 16 per cent of Afghan children are married under the age of 15, according to recent data from Unicef. And there is evidence that the poverty of recent years is pushing down the marriage age further in some areas.

Miserable union

The practice can force couples into a miserable union and sometimes expose the girl to violence if she resists.

Sunam's father committed her in marriage as a gift to his sister, Fahima, who does not have a daughter and desperately wants one.

"It's a very common problem. I know people in my own family who were engaged this way," said Orzala Ashraf, founder of Humanitarian Assistance for the Women and Children of Afghanistan.

"The engagement happens before birth in some cases."

The minimum legal age of marriage in Afghanistan is 16 for girls and 18 for boys. Yet child marriages account for 43 per cent of all marriages, according to the United Nations.

The reasons are often economic: The girl's family gets a "bride price" of double the per capita income for a year or more, according to the World Bank.

One 22-year-old woman from Kabul has tried to break off her engagement for eight years. Her 36-year-old fiance - whom she describes as uneducated, conservative and cruel, "like a Taliban" - has threatened to kill her if she refuses him.

She is educated and works for a prominent international organisation. Her fiance is a tailor with a high school diploma.

"I'm young. I want to go to school," she said.

Her voice was full of desperation and resignation.