30 million girls are at risk of female genital mutilation in the next decade, says UNICEF.
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.
Social acceptance is the most commonly cited reason for continuing the tradition, even though it is considered a violation of human rights, UNICEF found.
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 practiced 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 percent of females aged 15-49 have been cut, followed by 96 percent in Guinea, 93 percent in Djibouti and 91 percent 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.
In parts of Ghana, 60 percent of women in their 40s have undergone cutting, compared to 16 percent of teenagers.
In Togo, 28 percent of older women have been cut, compared to three percent of girls 15-19.
However, there was "no discernible decline in countries such as Chad, Gambia, Mali, Senegal, Sudan or Yemen," it said.
The report also found that even though the genital cutting is often considered a form of patriarchal control, there is a similar level of support among men and women for stopping it.
"Overall support for the practice is declining," said the report.
"Social norms and expectations within communities of like-minded individuals play a strong role in the perpetuation of the practice."
UNICEF said it should be open to greater public scrutiny, and called for groups that still practice the ritual to be exposed more to those that do not.
"The challenge now is to let girls and women, boys and men speak out loudly and clearly and announce they want this harmful practice abandoned," said Geeta Rao Gupta, UNICEF Deputy Executive Director.
Last year, the UN General Assembly adopted a non-binding resolution to intensify global efforts to eliminate female genital mutilation.