Sadr City under Siege?

I'm clearly missing something here:

Baghdad, Aug 30, (VOI)- Iraqi security forces have besieged Sadr City in eastern Baghdad and sealed off the city's main outlets, eyewitnesses said.

[...]

"Last night was calm and the city witnessed no clashes or unrest, so residents were surprised at today's siege," another eyewitness said.

The siege came one day after the decision taken by Shiite cleric Muqtada al-Sadr to freeze al-Mahdi Army for six months.

The decision was taken after recent speculation and accusations against al-Mahdi Army of being involved in the violent acts in the city of Karbala, where scores were killed and injured.

Wouldn't the declaration of a cease fire curb any supposed influence in Karbala? Wouldn't it be worth waiting at least a few days to see if this is true or not? Isn't this the kind of insult the security forces would want to avoid?