The White House has called the suicide bombing in Baghdad that killed 135 people an "atrocity" and pledged to help the Iraqi government bring security to the capital.
"The United States stands with the people of Iraq. We will support the freely elected Iraqi government and its security forces, to help bring those responsible for today's atrocity to justice, and to deliver greater security to the people of Baghdad," White House press secretary Tony Snow said in a statement
Yesterday attack was the deadliest single bombing in Iraq since the 2003 war.
A suicide bomber drove a truck laden with one tonne of explosives into a market in a mainly Shia area. The blast, which Shia Prime Minister Nuri al-Maliki blamed on Saddam Hussein supporters and other Sunni militants, shattered fruit and vegetable stalls, caved in shopfronts and left the smashed bodies of shoppers strewn in the street.
It came as US and Iraqi troops prepared for a planned offensive seen as a last-ditch effort to stem worsening sectarian bloodshed that kills hundreds in Baghdad every week.
"All Iraqis were shaken today by this crime,"Mr Maliki said in a statement in which he again spoke of his government's determination to crush the militants.
"The Saddamists and Takfirists (Sunni militants) have committed another crime."
Police said 305 people were wounded. The casualties swamped the capital's hospitals.
Three car bombs in the same market in December killed 51.