BAGHDAD — A mass grave with the remains of 12 people, including a paramedic who disappeared more than a year ago, was unearthed in an area long controlled by al-Qaida in Iraq, officials said Monday. In the capital, an Interior Ministry aide was gunned down in his car, police said.

Two of the decomposed bodies were beheaded, according to an official at Fallujah General Hospital, where the bodies were taken after their discovery on Sunday.

Hospital officials, who spoke on condition of anonymity because they were not permitted to release details of the discovery, said some appeared to have been killed as recently as four months ago, and some of the deaths dated to 18 months ago.

Along with the bodies was a Health Ministry card that belonged to the missing paramedic, according to footage from AP Television News.

Iraqi troops unearthed the bodies Sunday afternoon near Lake Tharthar, an area about 60 miles northwest of Baghdad where several mass graves were found in recent months. Since ousting extremists in some of the country's most violent areas, Iraqis from both Islamic sects have stepped up their patrols for the missing, leading to more discoveries.

Two other mass graves were found near the lake last month, one containing 40 bodies and another with 29 bodies. Elsewhere last month, a grave containing 17 corpses was unearthed near Baqouba, 35 miles northeast of Baghdad. Officials said at the time the bodies were likely those of people seized at fake checkpoints and killed because of their sectarian affiliation.

U.S. Deputy Secretary of State John Negroponte on Sunday pressed leaders of Iraq's religious and ethnic factions to take advantage of recent security gains to push through legislation aimed at cementing national reconciliation or risk a return to greater violence.

""If progress is not made on these fronts we risk falling back to the more violent patterns of the past," Negroponte said at a news conference in Baghdad.

The U.S. military has said violence in Iraq has fallen to lows not seen since January 2006, but top American commanders have warned that Sunni and Shiite extremists still pose a serious threat.

In Baghdad, gunmen in two cars fired on a Sunni Interior Ministry aide, Maj. Gen. Fauzi Hussein Muhammed, as he returned home, killing him and wounding his driver, police said. They spoke on condition of anonymity because they were not authorized to release details of the attack. The Interior Ministry could not immediately be reached for comment.

The mutilated bodies of four guards at an oil facility who were kidnapped at a checkpoint on their way back from vacation were found north of Baghdad on Monday, said Col. Khali al-Zubaie, an army spokesman in Kirkuk. A fifth man who disappeared with them remained missing, he said.

Political progress has been elusive, with lawmakers clashing over Kurdish oil deals with foreign companies and a draft bill that would allow thousands of former members of Saddam Hussein's Baath Party to return to their government jobs. Both measures are among the 18 benchmarks set by the Bush's administration to encourage reconciliation.

Oil Minister Hussain al-Shahristani, using unusually strong language, told Iraqi state television late Sunday that the contracts signed by the self-rule Kurdish region were illegal.

"No region has the right to go it alone and sign a deal," he said. "This will lead to the breakup of Iraq ... oil is the business of the federal government and any attempt at extracting oil without the approval of the federal government is tantamount to smuggling."

Jamal Abdullah, a spokesman for the regional government of Iraqi Kurdistan, said al-Shahristani's comments were unwarranted: "No one has the right to slander the legitimacy of contracts signed by the government of Kurdistan and the foreign companies."

During a meeting with Deputy Treasury Secretary Robert M. Kimmit, Prime Minister Nouri al-Maliki insisted the country's oil and gas resources belong to all Iraqis.

In a hopeful sign for political progress, lawmakers from Iraq's largest Sunni Arab bloc on Monday ended their boycott of parliament over the "house arrest" of their leader, Adnan al-Dulaimi, who also attended the session.

Al-Dulaimi was kept at home for more than two days after one of his guards was allegedly discovered last week with the keys to a car laden with explosives near his office in Baghdad. Al-Dulaimi's son and 30 other people were arrested.

The government has said al-Dulaimi, one of Iraq's most powerful Sunni Arab politicians, was prevented from leaving him home for his own safety. Defusing the crisis, the government moved him Sunday to a hotel near parliament in the heavily guarded Green Zone, also home to the offices of Iraq's government and the U.S. Embassy.