The head of the Supreme Council for the Islamic Revolution (SCIRI) in Iraq, Abd al-Aziz Hakim, escaped the attack, his son said in Tehran.
The bomber detonated a car bomb outside his office on Monday, Hakim's son Muhsin Hakim said, adding: "Abd al-Aziz Hakim and the other members of his family are safe and sound."
SCIRI has its offices in the Jadriya district in the south of the Iraqi capital.
"The car exploded at the gate to the offices, near the reception area," one official said, speaking on condition of anonymity.
"We took several guards and receptionists to the hospital," he added.
Ammar al-Hakim, a member of SCIRI's political bureau, accused members of Saddam Hussein's ousted government of being behind the attack.
"We have no doubts that remnants of the former Iraqi regime and their followers stand behind this attack," al-Hakim said.
"This alliance has expressed itself through many criminal and terrorist stances, killing our martyr Muhammad Baqir al-Hakim and many other national, Islamic and political figures," he said.
"We have no doubts that remnants of the former Iraqi regime and their followers stand behind this attack"
SCIRI political bureau member
"They have a criminal plan, which we have repeatedly mentioned before," he said. "However, intelligence information nowadays confirms the criminal intentions of this alliance," he added.
In August 2003, a bomber killed Ayat Allah Muhammad Baqir al-Hakim, elder brother of Abd al-Aziz and former leader of SCIRI.
Current leader Hakim also heads the candidate list of the 228-member United Iraqi Alliance coalition, which is expected to dominate Iraq's new constitutional assembly after elections on 30 January.
The coalition is supported by Iraq's top Shia cleric, Grand Ayat Allah Ali al-Sistani.
The residence, where Hakim has his home and offices, was previously the house of Tariq Aziz, the former deputy prime minister in Saddam Hussein's government who has been in prison since April last year.
National Guards abducted
Nearly two dozen troopers from the Iraqi National Guard may have been abducted by fighters in the west of the country, according to an account by a guard officer on Monday.
The interim defence ministry in Baghdad declined to comment on the report and no independent confirmation was available.
The officer said 21 men were seized as they returned by bus across the desert to their base at Qaim, close to the Syrian border, from Haditha, northwest of Ramadi and Falluja.
Iraqi National Guards are often
targeted by fighters
"They were all kidnapped," the officer said, quoting witnesses as saying armed men in several cars stopped the bus on the highway on Sunday afternoon.
He said he believed the attackers belonged to a group led by Jordanian self-declared al-Qaida ally Abu Musab al-Zarqawi, although it was not clear how this had been established or whether any demand had been made by the abductors.
On Monday, five men in civilian clothes were found shot dead
in Ramadi, the capital of Anbar province. A note said they were policemen killed by fighters.
There have been numerous other attacks on National Guards and police in the region and there have been instances of entire busloads being targeted.
Four Iraqi citizens have been killed and four others injured, all of one family, when a mortar landed on their house in al-Siniya district west of Baiji city, Aljazeera has learned.
The house was also badly damaged.