Three demonstrators died from bullet wounds and a fourth when a tear gas canister pierced his skull, medics and police sources told AFP.
"The security forces are getting closer to us, but the protesters are trying to hold them off by burning tires," a doctor in Tahrir told AFP.
"We can hear live fire now and there are so many wounded." Three protesters were killed and dozens wounded in the southern city of Basra, medical sources said, as security forces cleared a protest camp outside the provincial government headquarters.
Security forces also rounded up demonstrators in Basra.
And in the revered Shia holy city of Kerbala, south of Baghdad, the tents of protesters were reduced to ashes when security forces fired searing hot tear gas canisters at them.
The bloodshed came after political leaders agreed to rally around Prime Minister Adel Abdel Mahdi, whose embattled government was threatened by the largest and deadliest grassroots protests in Iraq in decades.
Abdel Mahdi, 77, came to power last year through a shaky alliance between populist cleric Moqtada al-Sadr and Hadi al-Ameri, a leader of the Hashed al-Shaabi paramilitary network.
When the protests first erupted in October, Sadr threw his weight behind them while the Hashed backed the government. But they closed rank around the premier this week after a series of meetings led by Major General Qasem Soleimani, the head of the Iranian Revolutionary Guard's foreign operations arm.