The attacks come at a time of political uncertainty in Iraq
By Gabriel Gatehouse
BBC News, Baghdad
Sadr City has over the past months become known as one of the safer neighbourhoods of Baghdad.
It is a sprawling area in the north of the capital with few entrances and exits. Those checkpoints are closely guarded.
Military and police officials have now stepped up security and are turning back vehicles.
But the measures came too late.
The damage has been done and many will be asking how the bombers managed to get through the checkpoints into this, almost exclusively Shia, enclave.
But the broader question is what the reaction will be, both in Sadr City and in the other predominantly Shia areas that were hit.
No group has publicly said it carried out the attacks, but many will look at the pattern of the latest bombings - all near groups of Shia worshippers and all around the time of Friday prayers - and draw their own conclusions.
Baghdad authorities have blamed al-Qaeda, saying the bombings were in revenge for the killing of high profile al-Qaeda operatives on Sunday.
In the absence of a claim of responsibility, it is difficult to confirm this theory.
But it is hard not to conclude that the attacks - whoever carried them out - were designed to inflame tensions between Sunnis and Shias.
In Sadr City, residents resisted the temptation to point the finger at the Sunni community.
Many said they blamed foreign fighters or the political wrangling that preceded and followed last month's inconclusive parliamentary election.
These attacks come at a time of uncertainty in Iraq.
Politicians are awaiting a recount of votes in Baghdad before they begin the process of negotiations to form a government.
It may be months before that process is complete. Then much will still depend on whether all of Iraq's various sectarian and ethnic groups feel included in the political process.
In the meantime it is feared that bombers will continue to try to destabilise the relative peace between Iraq's majority Shia and their minority Sunni rivals.
And while most people say they hope the days of sectarian bloodshed are behind them, memories of the vicious fighting which nearly plunged the country into full-scale civil war are still fresh.