At least two people have been arrested and a third interrogated in Anbar province, a Sunni-majority desert region in the country's west, after Facebook posts.

Protests demanding an overhaul of the political system have rocked Baghdad and southern Iraq, both mainly Shiite, but have not reached the west or Kurdish-majority north.

Residents of western Iraq have told AFP and HRW they were remaining quiet of out of fear of being accused of being "terrorists" or backers of ex-dictator Saddam Hussein.

But security forces there appear to be monitoring social media accounts, HRW said on Monday.

"Despite years of terrible conflict, many Iraqis have felt free to speak out on political issues," said HRW's Middle East director Sarah Leah Whitson.

"But these cases mark a disturbing change, if you contrast these men's entirely peaceful political statements with the completely inappropriate response by the Anbar authorities."

The watchdog said Anbar's security forces had detained three men within hours of their posts in support of the protests, which erupted on October 1.

Two of them were later released, while a fourth man had gone into hiding after being warned he was wanted for his Facebook posts.

Shortly after protests first broke out, Iraqi authorities imposed a total internet blackout for about two weeks.

They later banned social media sites including Facebook and popular messaging app WhatsApp, but Iraqis are widely using virtual private networks (VPN) to continue accessing them.

Security forces and unidentified assailants have also arrested hundreds of demonstrators in Baghdad and the south including from hospitals, according to the Iraqi Human Rights Commission and Amnesty International.

Most were later released but some remain missing, including medic Saba al-Mahdawi, who was abducted on Saturday night after returning from a protest.

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