Egypt detained a leading opposition figure and allies on Tuesday on charges of plotting to bring down the government, but opposition groups said the arrests aimed to stymie their preparations for parliamentary elections next year.
Zyad Elelaimy, a prominent member of the Social Democratic Party and the Civil Democratic Movement, was held along with at least three others, the interior ministry said in a statement.
Elelaimy, who was also a leading member of the 2011 protests that unseated longtime ruler Hosni Mubarak, was arrested minutes after leaving a friend's house in Cairo's Maadi district around 2:20 a.m., eyewitnesses said.
"About two minutes after he left we heard him calling us. We looked from our balcony and we saw him being pushed into a civilian car by a large number of people in civilian clothes," a friend, Soha Bayoumi, told Reuters.
"It seems that they were waiting for him, it was an ambush," Bayoumi added, saying that the people who arrested Elelaimy identified themselves as national security agents.
The interior later issued a statement accusing Elelaimy and seven others of involvement in a plan fomented and financed through Muslim Brotherhood leaders abroad "to carry out violent and disorderly acts against state institutions simultaneously with creating a state of revolutionary momentum."
In a statement, the Civil Democratic Movement (CDM), a coalition of Egyptian opposition parties and figures, denied Elelaimy and the others arrested had any connections with the Muslim Brotherhood, which is banned in Egypt.
One of Elelaimy's colleagues said he believed the arrest was linked to the coalition's move to seek more members to prepare for parliamentary elections next year.
"We have nothing to do with the Brotherhood … I am truly astonished and I don't know why security would be upset that we want to take part in the elections in the framework of the law and constitution," said CDM member Khaled Dawoud.
Human rights lawyer Gamal Eid said opposition figures Hisham Foad, Hossam Moeness and Hassan el-Barbarry were among those who had been arrested in recent days. They were being questioned at the state security prosecution headquarters, he said.
Since becoming president in 2014, former army chief President Abdel Fattah al-Sisi has overseen a far-reaching crackdown that has swept up Islamists and liberal opponents.
At least 60,000 people have been jailed, according to Human Rights Watch. Sisi has denied holding political prisoners and his backers say the measures were necessary to stabilise Egypt after its 2011 uprising.