A controversial child marriage law in Bangladesh which allows children as young as 14 to be married off by their parents was criticised by rights groups on Wednesday. Parliament passed the Child Marriage Restraint Act last night, replacing a law dating back to the British colonial period.

The new rule keeps the minimum marriageable age for males at 21 and for females at 18 but relaxes the restriction for "special circumstances" – including for girls who elope, are raped or bear children out of wedlock.

Rights groups have criticised the law, saying it would jeopardise the gains Bangladesh has made in cutting the levels of child marriage and improving the health of women and children.

"The biggest concern is the law has not set any minimum marriage age for special circumstances, meaning children can be married off at the age of 14-15," said Nur Khan Liton, who represents the Child Rights Advocacy Coalition in Bangladesh.

The coalition, which includes international charities such as Save the Children, Action Aid, national charities and rights groups, said the law could be abused and poses a "risk" to children.

But a ruling party lawmaker who heads parliament's committee on women's and child affairs said it reflects the reality in villages where 70 per cent of Bangladesh's 160 million people live.

"We have taken into account the opinion of the UNICEF and other experts," said Rebeca Momin, adding that the law also toughens penalties for people violating the minimum marriage age.

She said the special circumstances in the law are aimed at protecting rights and giving dignity to children born out of wedlock.

Despite making impressive gains in many social indicators in recent decades, child marriage remains rampant in the conservative Muslim-majority country.

Bangladesh currently has one of the world's highest rates of child marriage.

According to figures posted by UNICEF on its website, 66 per cent of girls are married before the age of 18 and over a third before the age of 15.

The previous child marriage law was widely ignored as parents in many poor districts were found to have married off their daughters at the age of 14.