BAGHDAD - Iraqi security forces detained hundreds of people, including prominent journalists, artists and intellectuals, witnesses said Saturday, a day after nationwide demonstrations brought tens of thousands of Iraqis into the streets and ended with soldiers shooting into crowds.

Four journalists who had been released described being rounded up well after they had left a protest at Baghdad's Tahrir Square. They said they were handcuffed, blindfolded, beaten and threatened with execution by soldiers from an army intelligence unit.

"It was like they were dealing with a bunch of al-Qaeda operatives, not a group of journalists," said Hussam al-Ssairi, a journalist and poet, who was among a group and described seeing hundreds of protesters in black hoods at the detention facility. "Yesterday was like a test, like a picture of the new democracy in Iraq."

Protesters mostly stayed home Saturday, following more than a dozen demonstrations across the country Friday that killed at least 29 people, as crowds stormed provincial buildings, forced local officials to resign, freed prisoners and otherwise demanded more from a government they only recently had a chance to elect.

"I have demands!" Salma Mikahil, 48, cried out from Tahrir Square on Friday, as military helicopters and snipers looked down on thousands of people bearing handmade signs and olive branches signifying peace. "I want to see if Maliki can accept that I live on this," Mikahil said, waving a 1,000-dinar note, worth less than a dollar, toward Prime Minister Nouri al-Maliki's offices. "I want to see if his conscience accepts it."

The protests - billed as Iraq's "Day of Rage" - were intended to call for reform of Maliki's government, not revolution. From the southern city of Basra to northern cities of Kurdistan, protesters demanded the simple dignities of adequate electricity, clean water and a decent job.

As the day wore on, however, the demonstrations grew violent when security forces deployed water cannons and sound bombs to disperse crowds. Iraqi military helicopters swooped toward the demonstrators in Baghdad, and soldiers fired into angry crowds in the protest here and in at least seven others across the country.

And in that way, the day introduced a new sort of conflict to a population that has been targeted by sectarian militias and suicide bombers. Now, many wondered whether they would have to add to the list of enemies their government.

Ssairi and his three colleagues, one of whom had been on the radio speaking in support of protesters, said about a dozen soldiers stormed into a restaurant where they were eating dinner Friday afternoon and began beating them as other diners looked on in silence. They drove them to a side street and beat them again.

Then, blindfolded, they were driven to the former Ministry of Defense building, which houses an intelligence unit of the Iraqi army's 11th Division, they said. Hadi al-Mahdi, a theater director and radio anchor who has been calling for reform, said he was blindfolded and beaten repeatedly with sticks, boots and fists. One soldier put a stick into Hadi's handcuffed hands and threatened to rape him with it, he said.

The soldiers accused him of being a tool of outsiders wishing to topple Maliki's government; they demanded that he confess to being a member of Saddam Hussein's Baath Party. Hadi told them that he blamed Baathists for killing two of his brothers and that until recently he had been a member of Maliki's Dawa Party.

Hadi said he was then taken to a detention cell, his blindfold off, where he said there were at least 300 people with black hoods over their heads, many groaning in bloody shirts. Several told him they had been detained during or after the protests.