The family of jailed British-Egyptian pro-democracy activist Alaa Abdel Fattah, who is on hunger strike, say they have received proof he is alive.
A letter to his mother written two days ago says he is "drinking water again" and "receiving medical attention".
"I can sleep today without nightmares," his sister said in response.
His family had not heard from him since he started refusing water on 6 November to coincide with the start of the COP27 climate conference in Sharm el-Sheikh.
Last Thursday, his mother said she had been told by officials at Wadi al-Natroun prison, north-west of Cairo, that he had undergone an unspecified "medical intervention with the knowledge of a judicial authority".
Prison authorities also denied his lawyer access on Thursday and again on Sunday despite permits being granted by the prosecutor general.
The public prosecution meanwhile said a medical report had shown Abdel Fattah to be in "good health", without providing any proof.
The 40 year old, who is imprisoned for allegedly "spreading false news", has become a symbol of the 60,000 political prisoners believed by human rights groups to be languishing in Egyptian jails. Egypt insists there are none.
This is the letter Alaa's mother received at the prison gates today. It's dated two days ago. This is all we have. #FreeAlaa #COP27 pic.twitter.com/UXxwoV9gpf
The short letter that Abdel Fattah wrote to his mother, Laila Soueif, is dated 16:00 local time (14:00 GMT) on Saturday.
"How are you, Mama? I'm sure you're really worried about me," it says.
"From today I'm drinking water again so you can stop worrying until you see me yourself. Vital signs today are OK. I'm measuring regularly and receiving medical attention."
Abdel Fattah promises to write a longer letter on the "day of provisions", and requests that his mother bring him an MP3 player, vitamins and effervescent salts to the prison.
"Today is the first day I've been able to take a proper breath in eight days," said his sister, Sanaa Seif, who is in Sharm el-Sheikh to lobby for his release.
"Now we know he's alive. I'd know his handwriting anywhere. But when I read [the letter] again and again it leaves me with more questions. Why have they been refusing his lawyer access to him, even with a permit?
"Why did they hold this letter back from us for two days? Is it just cruelty to punish the family for speaking up?"
Ms Seif noted that her brother was still on hunger strike, still being denied access to British consular officials, and that he was still "arbitrarily detained with no end in sight".
"Even with so much international attention on Alaa the Egyptian authorities can still just disappear him. He needs to be on a plane to London and only then will we allow ourselves to feel true relief."
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(July 2022) Alaa Abdel Fattah: 'He’s certain he’ll never come out of prison alive'
Abdel Fattah, who obtained British citizenship last year through his London-born mother, began a partial hunger strike seven months ago in a bid to pressure authorities to at least allow British diplomats to visit him.
With them continuing to refuse consular access or even acknowledge his British citizenship, he wrote in a letter on 31 October that he would only drink water until COP27 opened, and then stop even doing that.
As concerns about Abdel Fattah's health mounted, UK Prime Minister Rishi Sunak said he had called for his urgent release at a meeting with Egyptian President Abdul Fattah al-Sisi in Sharm el-Sheikh last Monday.
US President Joe Biden, French President Emmanuel Macron, German Chancellor Olaf Scholz and UN High Commissioner for Human Rights Volker Türk have also urged Egypt to free Abdel Fattah.
UK Foreign Secretary James Cleverly old Times Radio on Monday morning that he was keeping "a very, very close eye on this case".
"What we will do is we will keep working to secure consular access because he is British dual national and that is what we expect and we'll keep pushing to get resolution on this long standing and very difficult case," he said.
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