Their decision on Wednesday came a day after two Sunni Arabs participating in drafting the charter - committee member Mijbil Issa and committee adviser Dhamin Hussein al-Obeidi - were gunned down as they left a restaurant in Baghdad's Karradah district. A bodyguard was also killed.
Issa was among 15 Sunnis appointed to the committee last month to give them a greater voice in preparing the constitution, which is planned to be approved by parliament by 15 August.
Two Sunnis had already withdrawn, and with the death of Issa the others were considering withdrawing from the committee.
Kamal Hamdoun, a Sunni member, said the 12 remaining members would meet on Thursday with Sunni leaders and discuss the way forward.
The brother of Mijbil Issa wipes
away tears after funeral prayers
"Our membership has been suspended temporarily until tomorrow when we meet the committee that chose us," Hamdoun said. "We don't have security."
The head of the constitution drafting committee announced later on Wednesday that the committee will finish its work in two days.Recruitment centre attacked
A man strapped with explosives has blown himself up among a group of Iraqi army recruits in Baghdad, killing up to 10 people and wounding more than 20.
Police sources said the bomber mingled with the crowd of men outside a recruitment centre on Wednesday, at an abandoned airport in the Muthana district of central Baghdad, before detonating the explosives.
"Our membership has been suspended temporarily until tomorrow when we meet the committee that chose us. We don't have security"
Sunni member of the committee
About 10 people were reported dead and 22 injured, officials at al-Yarmuk hospital said.
Also on Wednesday, a key provincial leader in southern Basra was wounded in a morning attack, police said.
Husain Hamid, head of the municipal councils at the Basra governorate, was injured when armed men opened fire, said police Lieutenant-Colonel Karim al-Zaidi.
Hamid is said to be the number two leader in the Basra provincial government.
Meanwhile, Iraqis urged by the government observed a three minute silence at midday on Wednesday to remember "victims of terrorism" in Iraq.
The country commemorated the nearly 120 people killed in two of last week's most deadly bombings.
Police halted traffic in some streets of Baghdad, while pedestrians stopped at exactly noon (0800 GMT) to mourn the dead.
US helicopter downed
On Tuesday, Iraqi police said a US helicopter gunship came under gunfire and was shot down on Tuesday night.
"An Apache was shot down at 11pm on Tuesday when unidentified gunmen opened fire on it," said Lieutenant Muhammad Ahmad of the Taji police.
US troops and Iraqi police conducted a search operation after the attack, he said.
The US military however said on Wednesday, the helicopter was forced to make an emergency landing north of Baghdad, although no crew members were injured.
Iraqi police said the US helicopter
gunship was shot down
The military said no hostile fire was involved in the incident at night when the helicopter made a hard landing near Taji, about 20km north of Baghdad.
"We had a helicopter develop a maintenance problem and conducted a precautionary landing," said 3rd Infantry Division spokesman Lieutenant-Colonel Clifford Kent. "The crew was recovered last night."
Elsewhere in Iraq on Wednesday, two civilians were injured when a car bomb exploded as a US military patrol passed through the Toz Khormato area in Kirkuk city, Aljazeera learned.
In Mosul, police arrested Imad Abd al-Rahman, the leader of al-Mujahidin Brigades.
And an oil pipeline exploded in an attack in the western city of Samarra.