From a small blue tent pitched outside the UK’s Foreign Office, Sanaa al-Seif has been leading a one-woman protest in a bid to secure her brother’s release from an Egyptian jail as the Arab state prepares to host global leaders at the COP27 summit.

Like many Egyptians, she is hoping that the climate conference, which opens in the Red Sea resort of Sharm el-Sheikh on Sunday, will provide a rare chance to shine an international spotlight on the country’s dire human rights record.

“COP is an opportunity when eyes will be on Egypt — an opportunity to speak up and get some breathing room,” said Seif, surrounded by portraits of her incarcerated brother, Alaa Abdel Fattah. “It could save lives if the spotlight on the human rights conditions keeps escalating, and if governments put it in their engagement with Egyptian authorities.”

Abdel Fattah is one of the highest profile political prisoners among thousands detained by President Abdel Fattah al-Sisi’s regime since the former army chief seized power in a 2013 coup. And the attention his case has garnered in the lead-up to COP27 underscores how concerns over human rights threaten to cast a shadow over the summit.

Sanaa’s protest, and Abdel Fattah’s imprisonment, has already drawn the attention of climate activists — Greta Thunberg was among those who have visited her tented sit-in in a show of solidarity.

Amnesty International used a rare press conference in Cairo on Sunday to call for the immediate release of Abdel Fattah, who has been on a partial hunger strike for more than 200 days.

 “We are running out of time, so if the authorities do not want to end up with a death they should have — and could have — prevented, they must act now,” said Agnès Callamard, Amnesty’s secretary-general. “Twenty-four, 48 hours, 72 hours at the most — that’s all they have to save a life. If they don’t, that death will [hang over] COP27. It will be in every single discussion.”

Callamard added that despite the release of some 776 political prisoners this year, Cairo has arrested 1,500 more people since April.

“We will not be fooled,” she said. “The government cannot spin its way out of the situation. It must take concrete, visible, authentic actions.”

UK prime minister Rishi Sunak wrote to Sanaa Seif on Saturday saying the British government was “totally committed” to resolving Abdel Fattah’s case and that he “remains a priority”.

The 40-year-old, who was an icon of the 2011 revolution that ousted veteran president Hosni Mubarak, was granted British citizenship last year.

Dozens of British MPs have also raised his case in recent weeks, while 15 Nobel Prize winners in literature have lobbied for leaders to use the summit to address the issue of Egypt’s political prisoners.

Some activists say the scrutiny that has accompanied COP27 has already caused the regime to at least signal that it is sensitive to outside criticism ahead of the summit.

Hossam Bahgat, the head of the Egyptian Initiative for Personal Rights, an independent Cairo-based advocacy group, said the government had released about 800 political prisoners this year and also pledged to establish a political dialogue with civil society and opposition parties.

Those moves indicate a tentative shift for a government that is widely described as the country’s most autocratic in decades.

Bahgat said the number of those released from prison was more than in previous years, but added that it “still remains a small number relative to the overall population of political prisoners”.

“What’s more concerning is that new arrests on political charges didn’t stop going at the same pace, but it’s still a positive signal,” he said.

The problem, he added, was that the positive moves were just “very nascent steps that don’t constitute tangible or lasting change”.

For Abdel Fattah’s family, the fear is that time is running out as he has pledged to stop drinking water on Sunday.

“He was already looking very frail when I last saw him in August, so I don’t know how his body can endure any more,” Sanaa said.

Her brother has spent eight of the past 10 years behind bars. The activist is serving five years in prison after being convicted in December of “spreading false news that undermines national security” for a social media post.

Sanaa, who plans to attend COP27, was herself only released from prison in December after serving 18 months following charges of disseminating false news, inciting terrorist crimes and misuse of social media.

She worried that Sisi would use COP27 to project to his domestic audience that he is strong and enjoys the backing of western powers; she urged governments to take a stronger line on rights abuses.

“Whether the western politicians agree or not . . . this is how it’s being presented to us Egyptians and how it’s being used,” she said. “If Sisi feels his PR might be a little bit ruined, he would release some more.”

Despite his government’s human rights record, Sisi has enjoyed sound relations with western capitals that have traditionally viewed Egypt as an important Arab partner and vital to regional stability.

Former US president Donald Trump once jokingly described Sisi as his “favourite dictator”. The Biden administration has been more outspoken on human rights, but provided Egypt with $1.1bn in military aid last year, while withholding $225mn over rights concerns.

“We have made very clear to the Egyptian government our concerns about human rights issues in Egypt,” a State Department official said. “In particular, politically motivated arrests are a major challenge in Egypt.”

Bahgat said his concern was that once COP27 ends, the regime will return to its old ways, saying the small steps taken “could be very easily reversed . . . once the eye of the world is no longer on Egypt”.

Additional reporting by Felicia Schwartz in Washington