It appears that a putsch against the constitutional government of Iraq is underway in Baghdad. This seems to be on behalf of Nuri al-Maliki and against the newly elected Sunni Arab president of the country and the parliament. Maliki has been under great pressure from the US to leave office because it has been thought that he has largely been responsible for the alienation of many of Iraq's Sunni Arab population. He is said to have done this by opppressing that population as a means of advancing the interests of his own group, the Shia Arabs.
An alternative narrative of what is occurring is Maliki's claim that he is protecting the city against someone else's coup.
According to early reports large numbers of Ministry of Interior police troops (overwhelmingly Shia and loyal to Maliki) have taken control of the various bridges over the Tigris River that separate Shia East Baghded from largely Sunni West Baghdad. These police troops are reinforced by armored vehicles that must come from the Iraqi Army. They have moved in strength into the Green Zone which contains the US Embassy, the Parliament and various government facilities.
If Maliki wishes to seize control of West Baghdad it is difficult to see what would stop him. pl