United Nations human rights monitors have strongly condemned the state of Texas for its new anti-abortion law, which they say violates international law by denying women control over their own bodies and endangering their lives.

In damning remarks to the Guardian, Melissa Upreti, the chair of the UN’s working group on discrimination against women and girls, slammed the new Texas law, SB 8, as “structural sex and gender-based discrimination at its worst”.

She warned that the legislation, which bans abortions at about six weeks, could force abortion providers underground and drive women to seek unsafe procedures that could prove fatal.

“This new law will make abortion unsafe and deadly, and create a whole new set of risks for women and girls. It is profoundly discriminatory and violates a number of rights guaranteed under international law,” the human rights lawyer from Nepal said.

Upreti, one of five independent experts charged by the UN human rights council in Geneva to push for elimination of discrimination against women and girls around the world, was also sharply critical of the US supreme court.

Last week the court’s rightwing majority decided by a five to four vote to allow the Texas law to go ahead, despite the provision’s blatant disregard of the court’s own 1973 ruling legalizing abortion in the US, Roe v Wade.

“The law and the way it came about – through the refusal of the US supreme court to block it based on existing legal precedent – has not only taken Texas backward, but in the eyes of the international community, it has taken the entire country backward,” Upreti said.

Reem Alsalem, the UN’s independent monitor on violence against women, was also scathing of the supreme court’s decision to allow the Texas law to stand. The UN special rapporteur accused the five rightwing justices who formed the majority – who include all three of Donald Trump’s appointees – of exposing women to potential violence.

“Through this decision the supreme court of the United States has chosen to trample on the protection of women’s reproductive rights, thereby exposing them and abortion providers to more violence,” Alsalem told the Guardian.

Women of color, those with low incomes and from other vulnerable groups would bear the brunt of the crackdown, she pointed out.

Alsalem singled out as especially egregious the element of the Texas law that makes abortions all but impossible even for women who become pregnant because of rape and incest. “That exacerbates their trauma as well as mental and physical suffering.”

Chief justice John Roberts joined the three justices on the liberal wing of the supreme court in dissenting against the majority’s refusal to block the Texas law, with all four issuing strong statements.

Under SB 8 some 7 million Texan women are estimated to be at risk of losing access to legal abortions. Health clinics offering the service have already begun to turn patients away.

SB 8 bans all abortions after initial cardiac activity can be detected in the fetus, usually at around six weeks of pregnancy. Legislation to ban abortion so early are often evocatively but misleadingly called heartbeat bills, even though at that stage the heart has not yet formed.

The cut-off is so early that many women would not be aware that they are even pregnant, and up to 90% of all terminations in the state are expected to blocked.

Roe v Wade led the way to legal abortion up to the stage where a fetus can survive outside the womb, typically around 24 weeks into the pregnancy.

Another contentious aspect of the new Texas law is that it transfers responsibility for enforcing the new rules from state officials to ordinary citizens who are encouraged to sue anyone who “aids” or “abets” an abortion, with bounties of $10,000 and their legal fees paid if the lawsuit succeeds.

Under international law, governments are allowed to regulate voluntary terminations of pregnancy. But they are not allowed to do so in ways that jeopardize the lives or women, subject them to physical or mental pain or suffering, discriminate against them or arbitrarily interfere with their privacy.

Human rights bodies have long acknowledged that denying women access to abortion by criminalizing the practice or by erecting other hurdles can in certain circumstances amount to cruel, degrading and inhumane treatment. Abortion bans have even been likened by international bodies to a form of torture.

In 2015 the UN working group on discrimination against women conducted an official visit to the US to probe the position and treatment of women in American society.

In their final report, the human rights experts expressed regret that American women have “seen their rights to sexual and reproductive health significantly eroded… Ever-increasing barriers are being created to prevent their access to abortion procedures.”

Upreti told the Guardian that since that visit, the situation in the US had deteriorated further.

“We notified the US administration that the imposition of new barriers to access to abortion services constitutes discrimination under international law, yet the retrogression has continued,” she said.