Speaking to AFP using pseudonyms, they have described an apparent campaign of surveillance and intimidation by government forces and unidentified actors.
"We know we're all being followed, particularly the girls," said Mariam, a young female activist in the main protest site of Tahrir (Liberation) Square.
"Fake volunteers join us and take pictures of us, gather information and then disappear," she told AFP.
Since rallies demanding regime change resumed on October 24, protesters have occupied Tahrir day and night, squatting in abandoned buildings and spilling over onto nearby bridges.
They have established food distributions, street cleanings, a daily newsletter on protesters' demands and help for those wounded in clashes with security forces.
Mariam, for example, is responsible for keeping an inventory of available supplies and distributing donations streaming in from Iraq's various provinces and even outside the country.
She has been an active critic of the ruling class for years, slamming pro-Iran political factions and armed groups in social media posts.
Mariam told AFP she was told by well-informed sources that her name was included on a "hit list" of activists, journalists and rights defenders.
No such list has ever been published, but prominent activists have been assassinated by unknown assailants in Iraq's south, including two in Basra and two in Amara.
Agents 'rescue' fake protester
Dozens more have disappeared, including doctor and activist Saba al-Mahdawi and four other medics who had been providing care to wounded protesters in Tahrir.
Some were taken for just 24 hours, but others were missing for two full weeks before their captors dropped them off, disoriented, in random neighbourhoods at dawn.
Were they detained by government security forces? Their families said they never saw an arrest warrant.
Could the activists themselves tell who detained them? They're too scared to speak.
An intelligence source confirmed to AFP that undercover police officers had been working for several days to arrest activists in Tahrir.
"This is to scare them and force the rest to go home," the source said.
Mohammed, a medic, said fellow doctors had received threats on Facebook while others had been hailed down near Tahrir by people pretending to be protesters.
"It'd be better for you to stop," the men say, before disappearing in the crowd.
Other suspicious men have tried to provoke fights with security forces.
"Sometimes, one of them tries to incite violence and begins hitting a soldier," said Mohammed.
"But the rest of the protesters realise he's an infiltrator who wants to provoke them so he can arrest them after," he told AFP.
One police source admitted that undercover agents were being identified by protesters, including one officer caught while passing on information by phone.
"Our other guys had just enough time to come around pretending to be peaceful protesters and calling for an end to the violence," thereby rescuing him from the angry real demonstrators, this source said.
'We have seen worse'
Hala, another activist, said she noticed men intentionally trying to terrify people into leaving the square.
"In the middle of the night sometimes, when everything is calm in Tahrir, one man will start screaming to everyone to flee to send them into a panic," said Hala.
Those occupying the square ask anyone filming for their media accreditation, fearing they are undercover agents.
The threats and arrests are contributing to a "climate of fear" eerily similar to the rule of ex-dictator Saddam Hussein, when dissidents were disappeared by security forces or gunned down.
Activists and medics no longer commute to Tahrir alone, on deserted roads or at night and Mariam even avoids ambulances as they were used during Iraqi demonstrations in 2011 to abduct protesters.
Statistics on detentions are almost impossible to come by in Iraq and while most of those arrested by government forces have been released, others remain missing.
According to Amnesty International, the Hashd al-Shaabi paramilitary force has been involved in abducting at least one lawyer in the south.
It was founded in 2014 to fight the Islamic State group, drawing from a host of Shiite armed factions, many of which have close ties to Iran.
Hashd has publicly backed the government, slamming the protests as a "conspiracy" by outside powers.
Even those indirect messages are a threat, said Mariam.
"We know they're talking about us. We know those threats are directed towards us," she said.
But the generation now occupying the streets will not be so easily scared, she contended.
They grew up seeing corpses in the street during Iraq's sectarian violence, then lived through the horror of the Islamic State jihadist group.
"Those harassing us are well-trained, but they didn't think this through -- our generation has already seen worse," said Mariam.
"Their psychological war, it does nothing to us," she said defiantly.
