Several thousand men backing a paramilitary force close to Iran flooded the Iraqi capital's main protest camp on Thursday, worrying anti-government demonstrators who have denounced Tehran's role in their country.
The men arrived in Tahrir (Liberation) Square in apparently coordinated marches from different parts of the capital, waving sticks, Iraqi flags and the logo of the Hashed al-Shaabi armed network.
Some carried portraits of Hashed fighters killed in fighting against jihadists as well as pictures of the country's top Shiite cleric, Grand Ayatollah Ali Sistani.
The Hashed had backed the Iraqi government but after a dramatic intervention by Sistani last week, it dropped its support. The embattled prime minister, Adel Abdel Mahdi, resigned at the weekend.
Many units within the Shiite-majority force have been trained or equipped by Iran.
The demonstrators occupying the square for weeks have explicitly criticised Iran for backing an Iraqi political elite they see as corrupt and inept.
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They have insisted that all current figures in power are tainted with graft and have been wary of political parties seeking to coopt the youth-dominated movement.
The new arrivals on Thursday mixed in with thousands of other protesters in the square, who appeared worried although no confrontation or skirmishes took place.
"They've ruined it," one protester said, as another muttered, "It's going to get messy."