Boris Johnson has condemned a decision to scrap the constitutional right to abortion in the United States as a “big step backwards”.

The US Supreme Court has ended constitutional protections for abortion that have been in place for nearly 50 years by deciding to overturn the landmark Roe v Wade ruling.

It is expected to lead to abortion bans in roughly half of US states.

The Prime Minister told reporters at a press conference in Kigali, Rwanda, that the move was a “big step backwards”, adding: “I’ve always believed in a woman’s right to choose.”

Some UK groups have been quick to hit out at the ruling, with the British Pregnancy Advisory Service (Bpas) – the UK’s leading abortion provider – saying it is “appalled”.

Chief executive Clare Murphy said: “Banning abortion does not remove women’s need to end a pregnancy. It simply makes it more difficult and more dangerous.

“We are calling on the UK Government to publicly condemn this assault on women’s human rights, and make clear on the international stage that removing women’s access to swift, safe abortion services has absolutely no place in any society that calls itself civilised in the 21st century.

“For our politicians to watch silently as women’s rights are rolled back would be unforgiveable. We urge the Government to show leadership as a matter of urgency.”

Nimco Ali, the Government’s independent adviser on tackling violence against women and girls, called the decision “an assault on women’s human rights, their lives and their families”.

She tweeted: “The UK Government and other #G7 cannot remain silent as women’s human rights are breached.”

The Women’s Equality Party tweeted: “Make no mistake. Women will die because of this ruling, and tens of thousands more will be criminalised or forced to continue with pregnancies they did not choose.

“It is barbaric, inhumane and utterly heartbreaking. Solidarity with our sisters.”

The party and the campaign group Abortion Rights were calling for people to join them in protest at the decision outside the US embassy in Vauxhall, south London, on Friday evening.

Mayor of London Sadiq Khan posted on Twitter: “London stands with the women of America whose most basic rights and freedoms are threatened by this ruling.

“A dark day for a great country.”