The Mujahedin-e Khalq gunmen opened fire on the two men as they passed the group's Baghdad headquarters, apparently because the recently bought Mercedes belonging to the administrative attache, Caglar Yucel, was still carrying the previous owners' Iranian plates. Mr Yucel, 54, was killed and the embassy's communications officer was hurt by flying glass.
'It was a mistake. We have nothing against Turkey,' the group's leader, Massoud Rajavi, told Turkey's Hurriyet newspaper.
Iranian opposition groups have found limited sanctuary in Turkey in the past decade, and Turkish press reports say that Ankara was cracking down on them as a gesture of good faith after a recent agreement with the Islamic regime in Tehran to suppress separatist Kurds in each others' countries.
Iraq moved quickly to reassure its northern neighbour, telling Turkey that the diplomat's killers had been arrested and would be 'severely punished'.