The United States and Iran held a "frank and serious" first meeting today of a new committee set up by the arch foes to seek an end Iraq's sectarian violence.
Hours before the diplomats met, a truck bomber in a crowded residential area killed at least 33 people in their homes.
Establishing the security sub-committee has been the main achievement so far of new face-to-face contacts between Washington and Tehran -- enemies which have had no diplomatic ties for almost 30 years but were driven to the negotiating table by the threat of all-out civil war in Iraq.
The United States accuses Iran of fomenting unrest in Iraq by supporting Shia militias and supplying weapons such as armour-piercing bombs used to kill US troops. Iran denies it is responsible for violence and blames the United States for unleashing sectarian strife after its 2003 invasion.
Neither country has said precisely what it hopes to achieve at the talks, which were hosted by Iraqi officials in Baghdad and led by Marcie Ries, a senior diplomat at the US embassy, and Amir Abdollahian, the deputy head of Iran's mission.
After the talks, which lasted several hours, a US embassy official said they were "frank and serious, and focussed as agreed on security problems in Iraq." They would continue at a date to be agreed later.
The two countries also have long-running feuds over other issues such as Iran's nuclear programme, but officials say they have not been raised in the Iraq talks.