Sunni Arab members of a committee drafting Iraq's new constitution ended their boycott Monday, six days after they walked out to protest the assassinations of two fellow Sunni constitution framers.

Their decision lifted the threat that the country's new constitution would be a product of only two of three major Iraqi ethnic and religious groups, leaving out the Sunni Arabs (search) who form the core of the insurgency and thus failing to provide a hope for a political exit from the incessant violence gripping the country.

The killing continued Monday, with a suicide minibus bomb attack outside a hotel once used by American contractors killing at least 12 people and injuring at least 18, hospital officials and police said.

That followed a truck bomb attack outside a Baghdad police station Sunday that killed at least 39 people, many of whom survived the initial blast but died from their burns in the hospital overnight. That was the deadliest single attack in Iraq in a week.

Six of the 12 Sunnis on the committee rejoined their colleagues Monday morning at the closed-door meeting, said Baqir Hammoudi, secretary to Humam Hammoudi (search), the head of the committee.

Sunni member Ali al-Mishhedani (search) said the others were absent because they lived too far from Baghdad or had other personal commitments. He said the others were expected in Baghdad later in the day.

Saleh al-Mutlaq (search), another Sunni member, said the Sunnis would meet Tuesday to review the charter's preliminary draft.

The Sunnis had announced they were suspending participation in the committee to protest last Tuesday's assassination of Sunni committee member Mijbil Issa and adviser Dhamim Hussein al-Obeidi.

Sunni Arab participation in the drafting is considered essential in order to win approval for the charter among the country's influential minority, which forms the core of the anti-U.S. insurgency. The draft must be approved by parliament by Aug. 15 and submitted to the voters in an October referendum.

But following the assassinations, the 12 remaining Sunnis demanded an international investigation into the killings, better security and a greater Sunni role in deliberations. It was not clear whether all their demands had been accepted.

Meanwhile, the minibus attack Monday targeted a checkpoint outside the Sadeer Hotel. The victims were believed to have been Iraqi private security guards employed by the hotel. The dawn blast was followed by bursts of automatic weapons fire.

In March, Abu Musab al-Zarqawi's Al Qaeda in Iraq group purportedly posted a video on a Web site showing a huge explosion at the Sadeer Hotel that killed four and wounded 40 others, including 30 American contractors. Al-Zarqawi's group described the Sadeer as the "hotel of the Jew."

About three hours after the first attack, a second suicide bomber targeted a former Saddam palace being used by the Ministry of Interior police command, killing at least two and injuring 10. The attacker drove into the main entrance of the palace, police said.

That large explosion around 8:40 a.m. shook downtown Baghdad and sent up black plumes of smoke.

In other violence Monday, gunmen killed a family of four in Samarra as they waited on the street for a ride in the tense city north of Baghdad. Subhi Thamir Hussein al-Badri, his wife and two sons were gunned down, police Lt. Col. Ayoub Mahmoud said. The reason for the killing was unclear, police said.