Egypt's state security prosecutor on Saturday ordered a prominent activist detained for 15 days for investigation on charges of involvement with a banned group and inciting and taking part in illegal protests, rights lawyers said.
Haitham Mohamedeen, a leftist lawyer, was taken from his home on Friday, security sources said, the latest in a number of arrests of activists in recent weeks.
At least 20 people have been detained by security forces over protests against a rise in metro fares, and they are being investigated on charges that include disturbing the peace and obstructing public facilities.
Mokhtar Mounir and Mohamed Hanafi, two rights lawyers representing Mr Mohamedeen, said he was under investigation for "participating in the activities of a banned group while knowing its objectives" and "using the internet to incite terrorist acts", charges he denies. The prosecutor did not identify the banned group, Mr Hanafi said.
A judicial source confirmed Mr Mohamadeen's detention but gave no further comment.
Mr Mohamedeen had been detained at least twice in the past, once in 2013 on accusations of belonging to a secret organisation and spreading lies about the military, and again in 2016 for calling for protests against the transfer of two Red Sea islands to Saudi Arabia.
His detention follows those of other prominent activists.
State security prosecutors this week ordered Shady Ghazaly Harb, a leading opposition figure during the 2011 Arab uprising that toppled President Hosni Mubarak, held for 15 days for investigation over accusations including joining a terrorist organisation, according to state news agency MENA.
Last week, authorities detained Amal Fathy for 15 days for investigation on charges of insulting the state after she posted a video on social media criticising the government for failing to protect women against sexual harassment.
Campaigners say Egypt's human and civil rights record has deteriorated sharply under President Abdel Fattah El Sisi. Mr Sisi's supporters say his tough security policy is needed to ensure stability as Egypt recovers from years of political chaos and tackles economic challenges and an Islamist insurgency.
Mr Sisi this week pardoned more than 330 people, many of them young people jailed for demonstrating in recent years.