Police sources said two mortar rounds struck the headquarters of the US-led occupation while some employees were queuing before a checkpoint to enter the Ministry of Housing.
One person is reported to be still in serious condition.
Meanwhile in Najaf, the Supreme Council for Islamic Revolution in Iraq (SCIRI) accused Muqtada al-Sadr's al-Mahdi army of assassinating its former leader Muhammad Baqir Al-Hakim.
It said Baath elements and foreign fighters had infiltrated the leadership of al-Mahdi army.
SCIRI spokesperson Qasim al-Hashmi also accused Shia cleric Majid al-Khoai of plotting to assassinate SCIRI member Sadr al-Din al-Qabanchi on Friday.
Al-Mahdi army warned
Al-Hashmi warned that al-Mahdi militiamen would face grave consequences if they did not leave Najaf city soon.
In Falluja, an explosion wounded a number of US soldiers who were then evacuated as US helicopters provided cover.
On the roads leading to the town of Tarmiyah, 40km north of Baghdad three explosions targeted a US convoy, residents said.
And in the southern Iraqi city of Samawa, armed men attacked an oil tanker and set it on fire.
Six US soldiers were wounded in a car bomb east of a US military base in Tal Afar district in the northern Iraqi city of Mousl. The wounded were evacuated and treated in a military hospital, Aljazeera’s correspondent reported.
Amid the violence and threats, talks continued between members of Iraq's Governing Council (IGC) and US officials to fill the presidential position.
Mahmud Uthman, a Kurdish member of the IGC, told Aljazeera that Ghazi al-Yawar, current president of the IGC, al-Akhdar al-Ibrahimi, the UN envoy to Iraq and Paul Bremer, the US occupation administrator, were discussing possible individuals for the position.