The number of women and girls dealing with the consequences of female genital mutilation in the US is more than three times greater than previously thought, the Guardian can reveal.

Figures showing more than 500,000 women in the US are estimated to be at risk of or have been subjected to the practice have revealed the extent of FGM cases in the country.

Campaigners are now calling for immediate action to deal with the “state of emergency” for all girls at risk of FGM. The practice can cause recurrent infections, death during childbirth and elimination of sexual pleasure.

Unpublished draft figures from the Centers for Disease Control and Prevention, seen by the Guardian, show that since the last prevalence study was done in 1997 the number of women and girls living with or at risk from FGM in the US has increased from an estimated 168,000 to 513,000.

New figures from the Population Reference Bureau,due to be released on Friday – International Day of Zero Tolerance for Female Genital Mutilation (an annual awareness day sponsored by the UN) – are expected to reflect the draft CDC study, which is due to be published in the coming months.

The extent of female genital mutilation in the US has been exposed following pressure from campaigners, including a global campaign against FGM led by Jaha Dukureh, a 25-year-old mother from Atlanta, who was cut as a baby in her home country of Gambia. With the backing of the Guardian, Dukureh launched a petition last May successfully calling for a new prevalence study into FGM and for a working group to be set up.

“This is a huge moment – once we have proper data we can really start taking first steps to end FGM in the US,” said Dukureh. “I haven’t seen the CDC study but these draft figures appear to prove what we already knew: FGM is an American problem; we can’t keep on ignoring it; we can’t afford to leave these girls at risk.”

Dukureh said new figures would add momentum to the growing campaign to end FGM and put the White House under more pressure to act. “Getting these figures out there is very significant not only for me but for everyone who signed the petition, all the members of Congress who supported the campaign, and every woman and girl at risk,” she said. “I am so grateful to every single person who has supported this movement.”

Campaigners were shocked at the draft figures, which suggest the number of women at risk has tripled while the number of under-18s at risk has quadrupled.

Taina Bien-Aimé, executive director of the Coalition Against Trafficking in Women, and a longtime anti-FGM activist, said: “These figures reflect the consequences of indifference to human rights violations against girls and African girls in particular. For almost 20 years, the US government has known that thousands of girls were at risk of FGM and yet sat back and did nothing to tackle this violence.

“Now the numbers may have quadrupled among young girls and there is still no concrete plan to address it. The discourse cannot be about fearing to challenge someone’s religion or culture, but on the fundamental rights of girls as human beings. The 1997 report was a wake-up call we didn’t take seriously – this updated report is a state of emergency for every girl at risk.”

Carrying out FGM on a minor has been illegal in the US under federal law since 1996, and 22 states have passed their own FGM laws. Last year, through the Girls Protection Act, Congress closed a loophole which was allowing girls to be taken back to their family home country for “vacation cutting”. Only six states have outlawed vacation cutting.

The Guardian has spoken to several young American women who were taken overseas to be mutilated during school holidays. Campaigners believe the practice continues despite the change in the law.

Charlotte Feldman-Jacobs, gender programme director at the Population Reference Bureau, confirmed that the new FGM prevalence figures from the PRB, carried out in parallel with the CDC study, revealed a sharp increase in the number of women estimated to have experienced FGM. Both groups are likely to urge caution with the data, which is based on the prevalence of the procedure in the country of origin applied to females from those countries living in the US.

“There are many more girls and women at risk of FGM than there were a decade ago, by the very nature of immigration coming from countries where it is carried out,” Feldman-Jacobs said. “It’s very important to have these figures. Yes, there are laws in place but are we meeting the health needs of these women and girls? [These figures show] FGM is happening in New York, in Boston, it really brings it home that this is not just something that happens over there.”

Shelby Quast, policy director at the women’s rights organisation Equality Now, said that while the Obama administration had taken the first step towards setting up a working group to fight FGM in the US, the country now needed to “step up and take charge”.

She said: “This means implementing the law on FGM more effectively, but that also includes training professionals who come in contact with girls at risk or survivors, including health care workers, teachers and social workers.

“This is an extreme form of violence against children and has to be dealt with urgently and comprehensively if we are to effectively protect the next generation of girls.”

For the UN’s FGM awareness day on Friday, the US state department is urging people to post photographs of themselves holding up a zero sign, and using the hashtag #Togetherforzero.

Cathy Russell, Barack Obama’s ambassador for global women’s issues, said tackling FGM was one of her “top priorities”. “We know that female genital mutilation/cutting is deeply rooted in cultural and social norms. For Zero Tolerance Day we’ve launched a social media campaign to raise awareness of FGM/C and to break the silence around it. It’s important that we work closely with those in their communities who know how to do this [awareness] work and are doing it well.”