Egyptian authorities on Thursday arrested the executive director of a leading human rights group, the third member to be taken into custody in less than a week despite international criticism.
Security forces arrested Gasser Abdel-Razek at his home in Maadi, south of Cairo, and took him to an unknown location, the Egyptian Initiative for Personal Rights (EiPR) said.
It gave no further details.
On Sunday, security forces arrested the group's office manager, Mohammed Basheer, on charges including "joining a terror group" and "spreading false news".
EIPR said that Basheer was questioned by the Supreme State Security Prosecution about the organisation's work and a visit earlier this month to its Cairo office "by a number of ambassadors and diplomats" to discuss human rights.
And on Wednesday, Karim Ennarah, director of criminal justice at EIPR, was arrested while vacationing in Dahab, South Sinai.
Democratic party outrage
He too was taken by security officers to an undisclosed location, the group said.
The US, a close ally of Egypt, said it was "deeply concerned" by the detentions.
"The United States believes that all people should be free to express their beliefs and advocate peacefully," the State Department's bureau handling human rights said.
US President Donald Trump has stood firmly behind Egyptian President Abdel Fattah al-Sisi, whom he reportedly called "my favourite dictator", but President-elect Joe Biden has signalled that he will take a firmer line on human rights.
Lawmakers from Biden's Democratic Party voiced outrage at the arrests and urged Egypt to free the activists immediately.
"We cannot stay silent as human rights defenders are targeted and detained," said Representative Mark Pocan, co-chair of the Congressional Progressive Caucus.
Basheer was placed in pre-trial detention for 15 days and will be questioned at a later date, EIPR said.
Pre-trial detention can last up to two years under Egyptian law, but the period is often extended.
Rights groups estimate that some 60 000 detainees in Egypt are political prisoners.
These include secular activists, journalists, lawyers, academics and Islamists arrested in a sweeping crackdown on dissent under President Abdel Fattah al-Sisi.
Egypt has repeatedly denied accusations of human rights violations.
Earlier this month Foreign Minister Sameh Shoukry insisted, during a news conference with his French counterpart Jean-Yves Le Drian, that detentions in Egypt are within legal frameworks only.
"There is no arbitrary detention, there is only detention according to the law," he said, in response to a question by a reporter about political prisoners held in Egyptian jails.