By ROBERT H. REID
ASSOCIATED PRESS

BAGHDAD, Iraq (AP)

A suicide car bomber killed 22 people in northern Iraq on Tuesday after insurgents lured police to the scene by shooting an officer, officials said. A mortar shell fired at a U.S. ceremony sent the U.S. ambassador and the top American commander scurrying for cover.

The suicide bomber struck on a busy commercial street in Kirkuk, a mixed Arab, Kurdish and Turkoman city in an oil-producing region 180 miles north of Baghdad. About half the dead were police who rushed to the scene after gunmen killed a fellow officer.

In addition to the 22 dead, another 23 people were wounded, according to police Brig. Gen. Sarhad Qader.

The attack was the latest in a wave of spectacular suicide operations which have killed more than 160 civilians since Friday, most of them Shiites.

On Wednesday, gunmen wearing Iraqi army uniforms broke into the home of a senior Sunni leader on 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 candidate in the Dec. 15 election, the ministry official Maj. Falah al-Mohammedawi said. One of the slain man's brothers said the family has been attacked before.

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

The slayings follow a big push by U.S. officials to encourage Sunni Muslim participation in the Dec. 15 election, which will install the first non-transitional government in Iraq since the 2003 invasion.

Also Wednesday, the U.S. military announced a new operation by American and Iraqi troops in predominantly Sunni western Iraq. The operation in Ramadi, 70 miles west of Baghdad, was launched Tuesday to prevent insurgents from stopping the vote in that city, a U.S. military statement said. It is the third in the city since Nov. 16.

American military casualty tolls have been on the rise. In the latest reports, the U.S. command said a soldier was killed Monday by a roadside bomb near Habaniyah, 50 miles west of Baghdad.

Two other soldiers from Task Force Freedom were killed Saturday by small arms fire while on patrol in Mosul, 225 miles northwest of Baghdad, a U.S. statement said.

Those deaths raised the number of U.S. service members who have died since the Iraq war began in March 2003 to at least 2,096, according to an Associated Press count.

American officials sought to downplay the mortar attack on a U.S. ceremony transferring one of Saddam Hussein's palaces in Tikrit to Iraqi control. The officials said the lone shell failed to explode and did not interfere with the handover.

"This was an ineffectual attempt to stop the progress that goes on every day in Iraq," said Lt. Col. Barry Johnson, a spokesman for the U.S. command in Baghdad.

However, Arabic satellite television stations aired footage showing an American colonel ducking for cover as the shell whistled overhead. Fearing more were on the way, U.S. security hustled U.S. Ambassador Zalmay Khalilzad and the U.S. commander in Iraq, Gen. George Casey, into the palace while American infantrymen and an Apache attack helicopter searched for the source of fire. The ceremony resumed a few minutes later

The provincial governor, Hamad Hamoud Shagtti, received a symbolic key to the palace and a deputy governor raised the Iraqi flag. Dignitaries toured the palace complex, which Saddam ordered built for his mother in 1991 and which had served as a U.S. military regional headquarters until this month.

"Although 28 other coalition operating bases have already been turned over to Iraqi Security Forces control this year, the Tikrit Palace complex is the most significant transition of real estate thus far," a U.S. statement said.

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 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.

Al-Samaraei, a former head of military intelligence under Saddam, did not identify the caller, and it was unclear whether the overture represented a breakthrough.

Also Tuesday, U.S. Marines announced the end of a major operation to secure towns along the Syrian border used by al-Qaida to smuggle foreign fighters into Iraq. Ten U.S. Marines and 139 insurgents were killed in "Operation Steel Curtain," which began Nov. 5 with about 2,500 U.S. troops and 1,000 Iraqi soldiers, a military statement said.

U.S. commanders plan to establish a long-term presence in the area to prevent al-Qaida and its Iraqi allies from re-establishing themselves in the towns of Husaybah, Karabilah and Obeidi along the Euphrates River. They also want Sunni Arabs there to vote in the national elections without fear of intimidation.

In Baghdad, Iraq's anti-corruption commission said that members of the former government who are under investigation will not be allowed to run in the elections.