Iraqi security forces have shot dead at least 45 protesters after demonstrators stormed and torched an Iranian consulate, in what could mark a turning point in the uprising against the Tehran-backed authorities.
At least 29 people died in the southern city of Nassiriya when troops opened fire on demonstrators who blocked a bridge before dawn on Thursday and later gathered outside a police station.
Police and medical sources said dozens of others were wounded.
Four people were killed in Baghdad, where security forces opened fire with live ammunition and rubber bullets against protesters near a bridge over the Tigris river, the sources said, and 12 died in clashes in Najaf.
Anti-government protesters stand on a concrete wall erected by security forces to close Rasheed Street during clashes in Baghdad. Source: AAP
In Nassiriya, thousands of mourners took to the streets, defying a curfew to bury their dead after the mass shooting.
Video of protesters cheering in the night as flames billowed from the consulate were a stunning image after years in which Tehran's influence among Shi'ite Muslims in Arab states has been a defining factor in Middle East politics.
The bloodshed that followed was one of the most violent days since the uprising began at the start of October, with anti-corruption demonstrations that swelled into a revolt against authorities seen by young demonstrators as stooges of Tehran.
Iran closed the Mehran border crossing to Iraq on Thursday night because of security reasons, the semi-official Mehr news agency reported, citing a local border official.
In Najaf, a city of ancient pilgrimage shrines that serves as seat of Iraq's powerful Shi'ite clergy, the Iranian consulate was reduced to a charred ruin after it was stormed on Wednesday evening.
The protesters, overwhelmingly Shi'ite, accused the Iraqi authorities of turning against their own people to defend Iran.
Security force and civilians gather near the burned Iranian consulate in Najaf, Iraq. Source: AAP
Iran's foreign ministry condemned the attack and demanded "the Iraqi government's firm response to the aggressors".
So far, the authorities have been unyielding in response to the unrest, shooting dead hundreds of demonstrators with live ammunition and tear gas, while floating proposals for political reform that the protesters dismiss as trivial and cosmetic.
Prime Minister Adel Abdul Mahdi has so far rejected calls to resign, after meetings with senior politicians that were attended by the commander of Iran's Revolutionary Guards' Quds Force, the elite unit that directs its militia allies abroad.
