* Protesters storm Iranian consulate in Najaf
* Anti-government protests began in October
* Commander says will protect Shi'ite Muslim authorities
* Consulate attack shows intense anti-Iran sentiment (Updates death toll, adds bridge blockage, attack on compound)
By John Davison and Alaa Marjani
BAGHDAD/NAJAF, Iraq, Nov 28 (Reuters) - Iraqi security forces shot dead at least 28 protesters on Thursday after demonstrators stormed and torched an Iranian consulate overnight, in what could mark a turning point in the uprising against the Tehran-backed authorities.
At least 24 people died when troops opened fire on demonstrators who blocked a bridge in the southern city of Nassiriya before dawn on Thursday. Medical sources said dozens of others were wounded.
Four others were killed in the capital Baghdad, where security forces opened fire with live ammunition and rubber bullets against protesters near a bridge over the Tigris river.
The incidents marked one of the bloodiest days since the uprising began at the start of October with anti-corruption demonstrations that have since swelled into a revolt against authorities scorned by young demonstrators as stooges of Tehran.
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 overnight. Protesters accused the Iraqi authorities of turning against their own people to defend Iran.
"All the riot police in Najaf and the security forces started shooting at us as if we were burning Iraq as a whole," a protester who witnessed the burning of the consulate told Reuters, asking that he not be identified.
Another protester, Ali, described the attack on the consulate as "a brave act and a reaction from the Iraqi people. We don't want the Iranians."
But he predicted more violence: "There will be revenge from Iran, I'm sure. They're still here and the security forces are going to keep shooting at us."
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.
"CUT THE HANDS"
In a statement that suggested more violence was to come, the military commander of the Popular Mobilisation Forces (PMF), an umbrella group of paramilitary groups whose most powerful factions are close to Iran, suggested the overnight unrest in Najaf was a threat to Shi'ite clergy based in the city.
The paramilitary fighters would use full force against anyone who threatened Iraq's most senior Shi'ite cleric, Grand Ayatollah Ali al-Sistani, commander Abu Mahdi al-Muhandis said in a statement posted on the PMF website.
"We will cut the hand of anyone trying to get near al-Sistani," he said.
Fanar Haddad, senior research fellow at the National University of Singapore's Middle East Institute, said the government and its paramilitary allies could use the consulate incident to justify a firm response.
"It sends a message to Iran, but it also works to the advantage of people like Muhandis," he said. The paramilitaries could use the consulate incident as "a pretext to clamp down, and framing what happened as a threat against Sistani".
Sistani himself has appeared to back the protesters since the unrest erupted, calling on politicians to meet the popular demands for reform.
Authorities set up "crisis cells" in several provinces to try to restore order, a military statement said on Thursday. They would be led by provincial governors but include military leaders who would take charge of local security forces. (Reporting by John Davison, Alaa Marjani in Najaf, Baghdad newsroom; Editing by Janet Lawrence and Peter Graff)
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