Oklahoma's governor has signed one of the most draconian abortion laws in the country, just hours after a leaked Supreme Court draft opinion predicted the imminent end of legal abortion statewide.

"I am proud to sign SB 1503, the Oklahoma Heartbeat Act into law," Kevin Stitt stated Tuesday on Twitter.

"I want Oklahoma to be the most pro-life state in the country because I represent all four million Oklahomans who overwhelmingly want to protect the unborn."

Abortions after about six weeks are prohibited under the measure. It makes allowances for medical situations but not for rape or incest instances.

Supreme Court decision leaked.

Stitt's revelation comes after a leaked draft opinion indicated that the Supreme Court is poised to overturn Roe v. Wade, the 1973 decision establishing abortion rights in the United States.

If the court upholds the draft verdict, abortion regulations will immediately revert to state legislatures, with up to half anticipated to impose bans or additional restrictions.

For many women, the threat of losing abortion access across large areas of the United States means traveling hundreds of miles for the procedure or giving birth under terrible circumstances.

Republicans such as Stitt have fought for years to overturn Roe. Once former President Donald Trump chose three conservative judges, dramatically moving the Supreme Court's political balance to the right, it was only a matter of time.

Rival demonstrations

Meanwhile, demonstrators on both sides of the US abortion controversy exchanged chants, prayers, and posters outside the Supreme Court building on Tuesday, hours after the high court's draft judgment overturning the 1973 Roe v. Wade decision was leaked.

Dozens of people gathered on the sidewalk just beyond the courthouse's barred marble steps across the street from the US Capitol on Tuesday, boisterously but politely expressing a mix of support for and opposition to statewide abortion rights.

Earlier today, anti-abortion protesters outnumbered their opponents, beating drums and chanting into megaphones, "Pro-choice is a lie, babies never choose to die," and "Abortion is violence, abortion is oppression."

Several people knelt in prayer.

One man wearing a pink pro-Roe v. Wade sweater attempted in vain to muffle an anti-Roe protester's screams by placing his palm over her speaker.

Pro-abortion activists responded, "Off our bodies" and "abortion saves lives." Others carried banners that read "Abortion is healthcare" and "Abortion is not a dirty word." "Thou shall not steal my civil rights." read one placard displayed by a group identifying as Roman Catholics who support abortion access.

"I think it can be overturned, and then it's going to become a war on women's rights again," Chelsea White, a Roe v. Wade supporter outside the court, told the Reuters news agency.

"And abortions will resume in back alleys. Because abortion will never be prohibited. It will never go away. All they are doing is putting women's health at risk."