Emma Watson, Keira Knightley, and Dame Emma Thompson are among 76 actors, writers, business leaders and campaigners calling on governments to increase support and protection of women fighting for their rights around the world.

The letter, published in the Guardian to mark International Women’s Day on Friday, says women risk “backlash, censorship and violence” whenever they defend their rights or speak out over injustice.

Calling on leaders to fulfil their commitments to protect women, the signatories write: “Women in all their diversity – women of every nationality, race, ability, religion, sexual orientation and gender identity – need to have their voices heard and respected. Every woman should have the freedom to make her own choices and claim her rights. Yet, when women speak out, attempt to have a say in the decisions affecting their lives or defend their rights, far too often they are silenced, undermined and even endangered. Women are at risk of backlash, censorship and violence wherever they speak out, both online and offline. The expertise and experiences of women human rights defenders are not being recognised or trusted. Women are not being meaningfully consulted on issues that directly impact them. Women who speak out are facing all forms of violence and abuse. This has to stop.

“We call on governments to recognise and trust the expertise of women’s rights organisations and women’s movements, in particular those representing marginalised women; to counter the silencing of women’s rights activists; and to fulfil commitments to protect women human rights defenders by bringing to justice those that perpetrate violence, and strengthening the law in line with international human rights frameworks.”

The UN adopted a resolution to protect female human rights defenders in 2013, recognising that women are targeted not only for their activism but because of their gender. But last month, Michel Frost, the UN special rapporteur on human rights defenders, said women were facing increased repression and violence.

Presenting his annual report to the human rights council in Geneva, Frost said: “Women who dare to speak out for human rights are stigmatised and called bad mothers, terrorists or witches, silenced and marginalised from decision-making and can even be killed. It is particularly worrying that the hostility they face comes not only from state authorities, but also the media, social movements, their own communities and even their family,” he said.

Facebook Twitter Pinterest Protesters participate in a march against male violence towards women and girls held in London in December 2018. Photograph: Penelope Barritt/Alamy

The murders of Honduran environmental activist Berta Cáceres and Brazilian politician Marielle Franco are among recent high-profile cases of women killed for their activism.

“The issue of safety is real for women’s human rights defenders. Personal safety, safety of the organisations that work on women’s rights issues, and their families,” said Helen Kezie-Nwoha, the executive director of Isis-Women’s International Cross-Cultural Exchange, a Uganda-based organisation that documents abuses against women’s rights activists.

“People are burned out. You don’t drop out [of work] but it reduces your productivity, so you shut down, you can’t do anything because you need time to recuperate, but you don’t have that space.” Donors need to factor that into their support programmes, she added.

The signatories of the letter, including actors Sienna Miller, Carey Mulligan and Gillian Anderson, along with writers Chimamanda Ngozi Adichie, Philippa Gregory and Abi Morgan and business women Martha Lane-Fox and Dame Stephanie Shirley, said the time was ripe for action.

“As momentum behind the #MeToo movement continues to grow, we are witnessing unprecedented acknowledgement of the challenges women face. Now more than ever, we have an opportunity to overcome the systemic oppression that denies women their rights. It’s time to move on from conversations to action.”

The letter was initiated by Womankind Worldwide, a global organisation supporting women’s rights groups in Africa and Asia.

Facebook Twitter Pinterest ‘Women are at risk of backlash, censorship and violence wherever they speak out’: Kiera Knightley was among signatories to the letter. Photograph: Daniel Leal-Olivas/AFP/Getty Images

Caroline Haworth, its CEO, said the letter was a chance to show a “global level of solidarity” for women on the frontline.

“It’s fantastic for women we work with that they are supported by these women,” said Haworth. “Women’s rights are under threat like never before, with rising fundamentalism, financial crises and political turmoil.

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“Support for human rights defenders on the frontline is something everybody can relate to because they are fighting the fight for the rest of us. People really appreciate that. A lot of women put themselves at real risk of violence and harm for the work that they do.”

In a separate letter published to coincide with International Women’s Day, 45 activists from 15 African countries demanded more action to close the gender gap.

In the letter, addressed to world leaders, they wrote: “You promised to achieve gender equality and empower all women and girls by 2030, but at the current rate of progress this will take 108 years. This is unacceptable. We need genuine progress, not grand promises.”

The letter called on men to play their part to demand change, before concluding: “We’re not looking for your sympathy, we’re demanding your action. Because none of us are equal until all of us are equal.”

Other signatories to the letter, initiated by the advocacy group One, included Aya Chebbi, African Union youth envoy from Tunisia, Dr Stellah Wairimu Bosire of Kenya’s medical association, Scheaffer Okore, from the Pan African Chamber of Commerce, Memory Kachambwa, from Femnet – the African Women’s Development and Communication Network – in Zimbabwe, and Oluwaseun Ayodeji Osowobi, from the Stand to End Rape initiative in Nigeria.