It looks like the ceasefire is off. After nearly seven months of standing down,  Shiite hardline fighters from Moqtada al-Sadr's Mahdi Army clashed with Iraqi security forces in Basra today. The reaction in Baghdad was almost immediate: the Green Zone was pounded with mortars or rockets throughout the day and at least one office of the rival Badr organization was torched. Clashes were also reported in Kut and a handful of smaller cities in the Shia-dominated south. By sundown, a curfew was in place in Basra, Kut, Hilla, Diwaniya and Sadr City to keep the violence from spreading.

The fighting comes as little surprise. For months, there has been a tense standoff in Basra between the Mahdi fighters loyal to cleric al-Sadr, the Islamic Supreme Council in Iraq (ISCI) and the Fadhila party, an offshoot of the Sadrists. They have carefully carved out their turf: the Mahdi fighters have infiltrated the police force, the ISCI  Shiites control a handful of posts on the local governorate council and the Fadhila party holds the Basra governor post and dominates the security forces which protect the oil fields, Iraq's largest. There are nearly half a dozen smaller militant Shia groups, like Jundallah, who also claim influence in the city. In the past year, the tension between these groups has repeatedly spilled over to street violence. And, after British forces withdrew from their base within Basra last December, it was inevitable that the militias would clash with the Iraqi security forces who replaced them. The latest reports indicate that today's fighting has left at least 15 people dead and dozens more wounded.

The fighting kicked off early on Tuesday morning and appears to have been well-planned: Prime Minister Nuri Maliki, along with the ministers of interior and defense, were on hand in Basra to oversee the operation. With the British taking a backseat role, the operation could be one of the first decisive battles to determine how well the Iraqi security forces can stand up on their own. According to Basra residents, Iraqi security forces moved into a handful of neighborhoods controlled by the Mahdi Army, perhaps to set up small combat outposts similar to the ones American troops have built in hostile neighborhoods in Baghdad. Fighters quickly fanned out on nearby rooftops with AKs, RPGs and BKC heavy machine guns. Sharqiya TV showed footage of fighters with their faces wrapped in checked keffiyah scarves shooting mortars from city streets and running through alleys with sniper rifles. Baha al Araji, a prominent Sadrist parliamentarian, compared the government security operation to Saddam's crackdown on the Shia uprising in 1991. His boss, Sadr, issued a clear warning in a statement: "We call all Iraqis to strike as a first step and if the government doesn't respect the demands of the people we call for civil disobedience in Baghdad and other cities. Then we wait for the third step which comes when it is needed."

Dozens of Sadr supporters took to the streets of Baghdad earlier today in what was billed as a protest against the government's unfair crackdown on the movement. Some protestors carried signs that read, "No, no to government militias," a swipe at the rival ISCI and Dawa parties who dominate the security forces in the capital. Tensions have increased between rival Shia groups in the past week since a provincial election law was passed. The elections, scheduled for October, could redistribute the balance of power across the Shia south. "The ISCI and the Dawa parties are trying very hard to drag us into a confrontation with the occupation or the government forces," says Ali Mayali, a Sadrist parliamentarian who maintains that the movement's ceasefire is still in place. "The Sadr trend has been targeted since the beginning of the occupation. And now that the provincial elections are coming, the need to hurt us and our followers has increased. If legal elections would take place, the trend will prevail and they know that."

It's unclear how the fighting in Basra will play out but it is unlikely that the Mahdi Army, or any of the other militias in the city, will give up their turf without a tough fight. A fight that some city residents say is worth the cost. "I feel it is good for us to see the security forces cleaning the city from the armed groups," says Walid Abdul Hamid, a 31-year old medical tech in Basra. "I don't care if these groups are from the Mahdi Army or not. It is good to finish these fighters so we don't see them again in Basra."

With reporting by Iraqi staff