BAGHDAD, Iraq — Gunmen wearing Iraqi army uniforms broke into the home of a senior Sunni leader today and killed him, his three sons and his son-in-law on the outskirts of Baghdad, his brother and an interior ministry official said.

Khadim Sarhid al-Hemaiyem was the leader of the Sunni Batta tribe and the brother of a parliamentary candidate in the Dec. 15 election, the official, Maj. Falah al-Mohammedawi said. Another of the slain man's brothers said the family has been attacked before.

"A group of gunmen with Iraqi army uniforms and vehicles broke into my brother's house in the Hurriyah area and sprayed them with machine gun fire, killing him along with three sons and his son-in law," said his brother, Nima Sarhid Al-Hemaiyem. "His eldest son was assassinated one month ago in the Taji area, northern Baghdad, when unidentified men shot and killed him."

Al-Mohammedawi said government forces were not involved and the investigation was focused on insurgents.

"Surely, they are outlaw insurgents. As for the military uniform, they can be bought from many shops in Baghdad," he said. "Also, we have several police and army vehicles stolen and they can be used in the raids."

The Batta tribe is one of Iraq's largest Sunni tribes from the area north of Baghdad, where they are influential. Dozens of people went to al-Hemaiyem's home, where the bodies were laid out, wrapped in blankets before the funeral.

The slaying follows a big push by U.S. officials to encourage Sunni Muslim participation in the upcoming election, which will install the first non-transitional government in Iraq since the 2003 invasion. Some Sunni-led insurgent groups have declared a boycott of the election and have threatened politicians who choose to participate in it.

Also today, the U.S. military announced a new operation with Iraqi troops in predominantly Sunni western Iraq. The operation launched Tuesday in Ramadi, 70 miles west of Baghdad, is aimed at preventing insurgents from interfering with voting there, a U.S. military statement said. It is the third operation in Ramadi since Nov. 16.

A U.S. official close to the trial of ousted dictator Saddam Hussein and seven others for a 1982 massacre of Shiites said the court expects defense lawyers to attend next week's hearing, despite their threat to boycott the trial.

The official told a news briefing that the court has "standby" defense lawyers to step in if the defense team makes good on its threat to boycott the Nov. 28 hearing, the first since the trial opened Oct. 19.

The threat followed the assassination of two members of the defense team since Oct. 19. They have since demanded protection for themselves and their families, as well as a U.N. investigation into the killings.

In other violence on Tuesday, gunmen blocked the road leading to the Communist Party's branch office in the mostly Shiite neighborhood of Sadr City in Baghdad just after the party began its election campaign, the party said in a statement. The unidentified men broke into the party building and killed two activists in the reception area, it added.

"This cowardly act coincides with our preparations for the upcoming election and it targets the political process," the party said. "The government should bear the responsibility of providing the necessary protection in order to ensure a safe atmosphere for the elections."

In a positive development, a senior government official said a representative of an unidentified insurgent group responded to an offer by President Jalal Talabani to talk with those willing to lay down their arms.

Presidential adviser Lt. Gen. Wafiq al-Samaraei told Qatar's Al-Jazeera television Tuesday night that he had received a call from someone "who claimed to be a senior official of the resistance."

"I informed him that I would welcome him in a meeting to hear from him, but this doesn't indicate our acceptance of their demands," he said.