Dhari Ali al-Fayadh, a member of the ruling Shia-dominated political alliance, his son and bodyguards were killed by a car bomb attack on their convoy in the northern outskirts of Baghdad on Tuesday, police sources said.
The group was hit while travelling from their farm in Rashidiya, some 35km northeast of Baghdad, said legislator Hummam Hammoudi, who heads the parliamentary committee charged with drafting Iraq's new constitution.
Al-Fayadh, 87, was the eldest member of the new parliament that was installed about three months ago and he had acted as speaker until one was elected.
He was a member of the country's largest Shia political party, the Supreme Council of the Islamic Revolution in Iraq. The party is the senior member in the ruling coalition.
He was also a senior shaikh from al-Boamer tribe, which includes both Sunni and Shia clans.
Al-Fayadh's relatives gather at
the scene of his death
He is the second member of Iraq's newly elected parliament to be assassinated since the Shia- and Kurdish-led government took office.
Violence in Iraq has worsened dramatically since the government took office. Lamia Khadori, another parliamentarian, was gunned down at her home in April.
In the hospital attack, a police spokesman said the bomber dressed in a police uniform blew himself up on Tuesday at the police guard station inside the medical facility in the town 75km south of Baghdad.
One of those killed and four of the injured were police officers, he added.
He said it was not clear whether the bomber was a policeman or used the police uniform as a disguise.
Bombings by attackers in police or military uniform have become an increasing threat in Iraq.
Also on Tuesday, police opened fire on a crowd of demonstrators in the southern Iraqi city of Samawa, killing at least one protester, Reuters witnesses at the scene said.
US troops have launched a new
offensive in western Iraq
A Reuters correspondent said nearly 2000 unemployed Iraqis were demonstrating because they had not been given jobs in the police in Samawa, 270km south of Baghdad.
Protesters threw stones and police opened fire, first with warning shots, then with shots aimed at the crowd.
Reuters photographer Mohammed Amin said he saw three demonstrators injured and one killed by a bullet to the head.
US soldier killed
Elsewhere in the country, a US soldier was killed by a bomber near Balad, north of Baghdad, on Tuesday, the military said in a statement.
The soldier died "when a suicide vehicle-borne improvised explosive device detonated near a coalition forces base", the statement said, adding that a second soldier was being treated for wounds suffered in the blast.
Meanwhile, more than 1000 US troops and Iraqi forces launched Operation Sword on Tuesday in a bid to crush fighters in western Iraq, making it the third major offensive in the area in recent weeks.
The new campaign is focusing on communities living along the Euphrates River between the towns of Hiyt and Haditha in al-Anbar province, said marine Captain Jeffrey Pool, a US military spokesman.
Operation Sword, or Saif in Arabic, comes on the heels of two other offensives - dubbed operations Spear and Dagger.