BAGHDAD - A suicide bomber drove through a checkpoint and blew up his car in Baghdad's Shiite district of Sadr City, killing at least 12 people in an attack apparently aimed at a nearby market, police and hospital officials said.

Iraqi police fired at the attacker after he refused to stop at the checkpoint, but he managed to detonate the explosives, officials said. Thirty-five people were wounded and many cars and shops were destroyed.

AP Television News video footage of the aftermath showed the burned out and twisted wreckage of three cars — the attack vehicle and two others beside it, one flipped onto its roof — across the street from a police station. Pools of water from fire hoses were stained with blood.

Meanwhile, a small Sunni Arab bloc ended its parliamentary boycott Saturday, returning to the legislature as it considers key benchmark legislation demanded by Washington amid increasing pressure to end the political deadlock.

The return of the Iraqi National Dialogue Front ends the last boycott of parliament, which had contributed to the political paralysis.

The party returned in part because parliament granted its demand that Shiite Prime Minister Nouri al-Maliki be summoned for questioning by lawmakers about the security situation in Iraq.

"We need a liberal government, we need a secular government. Without such a government the violence will continue," party head Saleh al-Mutlaq said from Jordan on Al-Jazeera television.

Al-Mutlaq said he considered a recent decrease in violence a "temporary improvement."

"The violence will grow again, as people will lose hope if nothing changes on the political side," he said. "There was a big failure on the political side ... without reconciliation the violence will not stop."

Elsewhere, the U.S. military said it had brought a new weapon into the fight in Iraq, announcing the Army's first-ever use of a drone aircraft to kill enemy fighters in the country.

The Hunter unmanned aerial vehicle, or UAV, dropped a precision bomb on two suspected insurgents believed to be preparing to plant roadside bombs on Sept. 1, the military said. The drone was called in for the attack near Qarraya, 180 miles northwest of Baghdad, after a scout team from the 2nd Battalion, 25th Aviation Regiment, observed the insurgents at work.

"This accomplishment adds a precise and discriminate means for our Army to successfully engage the enemy in counterinsurgency warfare," Col. A.T. Ball, commander of the 25th Combat Aviation Brigade, said in a statement.

In other violence Saturday, a bomb went off midday at a crowded market in the Shiite holy city of Kufa, 100 miles south of Baghdad, killing four people and injuring five, said Khalil al-Yasiri, a health official in the neighboring city of Najaf.

"I was shopping with my child Ameer, when a big explosion went off in front of us," said Salah Mihsin, 35, as he lay in his Najaf hospital bed, both legs injured. "I still don't know the fate of my child."

Gunmen in Najaf also killed Mohammed al-Qarawi, director of tribal affairs in anti-American cleric Muqtada al-Sadr's office. The local police commander Maj. Gen Abdul-Karim al-Mayahi said the attack occurred Friday on the road between Kufa and Najaf.

And in the north, the bodies of four Sunni Arabs gunned down on their way home Friday from a funeral were found, about 75 miles south of Kirkuk, while two bodies of Kurds with signs of torture were found in a village 10 miles north of the city, Brig. Sarhat Qadir said.

Though sectarian violence has been down in recent weeks, the attacks reinforced the obstacles to U.S. goals ahead of a report to Congress by the top U.S. commander in Iraq, Gen. David Petraeus, and U.S. Ambassador Ryan Crocker. The two are to attending hearings starting Monday on progress in Iraq since the introduction of 30,000 more American troops, including whether advances are being made toward national reconciliation.

Parliament reconvened Tuesday after a monthlong summer break but has not yet taken up any of the key benchmark legislation because competing factions have still not been able to hash out compromises.

Shiite, Sunni Arab and Kurdish leaders agreed in principle on some of the 18 issues that the U.S. has set as benchmarks for progress. Among them were holding provincial elections, releasing prisoners held without charge and changing the law preventing many former members of Saddam Hussein's Baath Party from holding government jobs and elected office.

The so-called de-Baathification draft law appears to be the closest to being ready.

"We will receive it today or tomorrow and then it will be put forward in parliament for discussion this week," deputy parliament speaker Khaled al-Attiyah told The Associated Press by telephone.

Al-Attiyah did not say how long he expects the discussion to last or whether it will be approved.

But he has previously said he did not expect to parliament to begin discussing another key draft law — on oil revenue sharing — before mid-September.

Separately, the British military said it was withdrawing 500 troops from Iraq as part of its planned reduction in forces as Iraqis assume control of security in southern Iraq.

The announcement came six days after British soldiers pulled back from their last base in Basra and moved to the local airport about 12 miles to the north. -AP