More than 125 million girls and women have undergone female genital mutilation, and 30 million more girls are at risk in the next decade, UNICEF says.
Although genital cutting is on the decline, the practice remains "almost universal" in some countries, said the UN Children Fund's report that spans 20 years of data across 29 countries in Africa and the Middle East.
The tradition involves removal of some or all of a female's external genitalia. It can include cutting out the clitoris and sometimes sewing together the labia.
Laws are not enough to stop the practice entirely, and more people must speak out in order to eliminate it among certain ethnic groups and communities, the researchers said on Monday.
Social acceptance is the most commonly cited reason for continuing the tradition, even though it is considered a violation of human rights, UNICEF found.
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The practice "is becoming less common in slightly more than half of the 29 countries studied", said the report.
However, the tradition remains "remarkably persistent, despite nearly a century of attempts to eliminate it", it said.
"As many as 30 million girls are at risk of being cut over the next decade if current trends persist."
The ritual is practised by various faiths, including Christians, Muslims and followers of African traditional religions. Some believe it improves a girl's marriage prospects, or that it is more aesthetically pleasing.
The report found the highest rates in Somalia, where 98 per cent of females aged 15-49 have been cut, followed by 96 per cent in Guinea, 93 per cent in Djibouti and 91 per cent in Egypt.
The amount of data for analysis varied from country to country, but some declines, even slight ones, were apparent over time.
"In Kenya and the United Republic of Tanzania, for example, women aged 45-49 are approximately three times more likely to have been cut than girls aged 15-19," said the report.
Prevalence of genital cutting among teenage girls has dropped by about half in Benin, the Central African Republic, Iraq, Liberia and Nigeria.
However, there was "no discernible decline in countries such as Chad, Gambia, Mali, Senegal, Sudan or Yemen," it said.
Last year, the UN General Assembly adopted a non-binding resolution to intensify global efforts to eliminate female genital mutilation.
