Heavy fighting erupted earlier today in the southern Iraqi oil city of Basra as Iraqi security forces launched a major operation against rival Shiite militias. The fighting could lead to the end of a seven-month-old ceasefire by Muqtada al-Sadr’s Mahdi Army. Earlier today, an official from Sadr’s headquarters reportedly ordered Mahdi Army field commanders to go on high alert and prepare “to strike the occupiers” and their Iraqi allies. The ceasefire by Sadr’s Mahdi Army has been seen as a major factor behind the recent drop in violence in Iraq. Basra is Iraq’s second largest city and Iraq’s gateway to the Gulf. Its oil fields are the source of most government revenues. The military operation was launched after Iraqi Prime Minister Nouri Al-Maliki visited Basra and vowed to reimpose his government’s control over the city.