On International Women’s Day, we celebrate the many achievements of women and stand together to demand equal rights. More and more people worldwide are speaking out against injustices and joining the fight for equality.

My sister, Loujain, is one of these brave gender equality activists – and for that she is now in jail. She has dedicated her life to gaining basic women’s rights in our home country of Saudi Arabia, focusing mainly on the women’s driving ban, male guardianship and domestic abuse.

But instead of marching on International Women’s Day, she is in prison. She has spent the last 10 months in a Saudi jail. She has told us she has been subjected to brutal torture and sexual harassment.

How can we achieve women’s equality if we allow its greatest advocates to die in jail? This sends the message to women worldwide that we won’t be there to protect you if like my sister you speak out. This will inevitably lead to the most vulnerable women remaining silent.

For many years, I was ignorant about the plight of women in my country because I believed they were treated the same as those in our family. Loujain opened my eyes by sharing horrifying stories of women being abused in their own homes. She was so passionate about this cause that she was about to open a domestic abuse shelter, just before she was arrested.

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Human rights organisations such as Amnesty International and Human Rights Watch have demanded action on the torture allegations. The US and British parliaments have passed resolutions to get a response from the Saudi government, and the European parliament has urged Saudi Arabia to release women’s rights campaigners from prisons. Several media organisations have shared Loujain’s story. And yet, the Saudi government continues to deny allegations of unlawful arrest and torture. Such denial proves we must keep the spotlight on my sister’s case.

This year has been a nightmare for my family. On the day of my sister’s arrest, my parents’ house was raided by armed men without a warrant. They took Loujain and for an entire month we had no idea where she was. No one would give us an answer on her whereabouts.

Things have only got worse since then. Loujain told us she has been beaten, electrocuted and sexually harassed. She was attacked by interrogators who tried to take off her clothes, telling her she is a slut. And one of the interrogators was found was found sitting next to her legs while she was asleep.

During a recent visit, we learned from Loujain that her captors had taken her to a psychologist to help her recover from torture she had endured. But she fainted from the trauma of reliving her experiences. On her second visit to the psychologist she says she was blindfolded and duct taped to a wheelchair.

The Saudi government claims the torture did not happen, but it cannot prove this because it won’t allow independent parties to visit the prison. It also claims to be reforming the country and promoting it as an open and tolerant nation that welcomes top musicians to play concerts and uses supermodels in tourism ads. But how can we claim we are opening up to the world when we don’t even respect basic human rights?

I was confused last month when Saudi Arabia announced the appointment of Princess Reema bint Bandar as the first female ambassador to the US. Was the intention to make real reforms for women and to empower them? When I see many women’s rights advocates languishing in jail, such intentions are hard to believe. If the country wants real reform, my sister should be freed.

Instead, after she has been held for nearly a year without charge, the public prosecutors recently announced that Loujain and other women will be put on trial for destabilising national security and dealing with foreign entities. This was announced right after Loujain was “forced” to sign a royal pardon for her release. How did she attempt to destabilise national security, and who are these foreign entities? The only thing my sister is guilty of is trying to protect other women.

On International Women’s Day we need to speak up for Loujain and other activists who have paid a high price for championing women’s equality; and to show that women’s rights advocates are stronger when they stand together. It is the day to transform words into actions. So please stand with Loujain, because standing with Loujain means getting one step closer to gender equality.

• Walid al-Hathloul is the brother of Loujain al-Hathloul and campaigning for the release of his sister from a Saudi jail