Bahrain has stepped up arrests of cyber activists and political workers, with more than 300 detained and dozens missing since security forces broke up street protests earlier this month.

Mattar Ibrahim Mattar, a member of Bahrain’s largest opposition group, Wefaq, said the party’s official arrest count was 329 by Thursday, but that the real number was likely to be more than 400.

He said at least 20 people had been detained on Thursday and 31 were missing. It was unclear if those people were in hiding or had been abducted.

There have been several reports of missing people who have turned up dead days later, but activists say that many of their peers are also going into hiding to avoid arrest.

Prominent Bahrain blogger Mahmood Al-Yousif was detained on Wednesday and released late on Thursday.

“I’m back home now with my family. Everything is fine,” he told Reuters by telephone. “I’ve been treated well enough. They investigated me but didn’t find anything,” he said.

Opposition sources said Abdul Khaleq Al-Oraibi, a doctor at Salmaniya Hospital, Bahrain’s biggest, had also been detained.

Oraibi, who once considered running as a member of Parliament for Wefaq, had been publicly critical of the lack of access for medics to wounded protesters.