Iowa has started enforcing a ban on abortions after six weeks of pregnancy, becoming the 22nd state to impose broad restrictions on ending pregnancies since the US Supreme Court overturned federal abortion rights in 2022.

Iowa's state Supreme Court ruled against a challenge by Planned Parenthood last month to stop enforcement of the law, which bans abortion before many women know they are pregnant while allowing exceptions for rape cases, medical emergencies, and fatal fetal anomalies.

The law was passed in a special legislative session in 2023, after the state Supreme Court failed to revive a separate 2018 abortion ban.

The legislature's Republican majority rebuffed efforts by Democrats to expand the law's exceptions, including a proposal to allow abortions for pregnant children aged 12 or under.

Until Monday, abortion was legal in Iowa up to 20 weeks.

It was a celebratory occasion for Maggie DeWitte, the executive director of anti-abortion organisation Pulse Life Advocates.

DeWitte told Reuters in an interview that her group hoped the state's conservative legislature would pass an even stricter ban in its next session.

"Our end goal, our gold standard, has been and will continue to be protecting all life from the moment of conception," she said.

Pro-abortion rights advocates and groups vowed to continue fighting for abortion rights at the ballot box and by assisting those seeking abortions.

"Iowa will be the 22nd state with an abortion ban in effect. These bans, imposed by Republican elected officials, put women's health and lives in jeopardy," White House Press Secretary Karine Jean-Pierre said in a statement on Monday.

Abortion is a major campaign theme for Democratic candidates in this year's elections. Bans enacted in Republican-led states have proven to be unpopular with a majority of Americans.

Vice President Kamala Harris, the likely Democratic nominee for president in November's match-up against former President Donald Trump, said in a statement on X that Iowa's ban ushered in a "health care crisis for women across the state."

Ruth Richardson, president and CEO of Planned Parenthood North Central States, said it was a sad day for women in Iowa.

"Our hearts are heavy as Iowans have lost the ability to make personal, private medical decisions," she said in a statement.

Planned Parenthood said it was prepared to help Iowa women who wanted an abortion travel to its clinics in Nebraska, where abortion is banned after 12 weeks, and Minnesota, where abortion is not restricted based on gestational duration.