A suicide bomber killed at least 23 people and wounded 72 on Friday at a gathering of Sunni Arab tribal leaders for a lunch in a town south of the Iraqi capital Baghdad, security spokesman Major-General Qassim Moussawi said.
The bombing took place a day after the United States presence in Iraq officially came under an Iraqi government mandate for the first time, according to a bilateral security pact that took effect on New Year's Day.
An Iraqi security source said Sheikh Mohammed Abdullah Salih, a Sunni leader of the al-Qaraghouli tribe, hosted the lunch at his home on the outskirts of Yusufiya, 20 km (12 miles) south of Baghdad.
The bomber, a relative of the host named Amin al-Qaraghouli, entered through the rear gate of the house and blew himself up among the guests, Moussawi said. The sheikh was among the wounded.
Violence has dropped sharply in Iraq from the peak of sectarian bloodshed in 2006 and 2007, but suicide bombers and gunmen still regularly stage attacks.
In the biggest recent attack, a suicide bomber killed around 50 people at a packed restaurant near the northern city of Kirkuk on Dec. 11. An attack in Baghdad last week killed at least 25 people.
Sunni Arab militants have frequently targeted tribal gatherings since many tribes turned against insurgents.
Almost six years after the U.S-led invasion, more than 140,000 U.S. troops in Iraq are gradually reducing their activities ahead of an end-2011 departure deadline.
U.S. forces handed over control of the Green Zone, the fortified swathe of central Baghdad that was the heart of U.S. power in Iraq since 2003, to Iraqi forces on Thursday.
Combat troops are supposed to leave Iraqi towns and cities by mid-2009.
But the United States is still providing major military, administrative and financial backing to Iraq.
Britain on Thursday formally handed over responsibility for the running of Basra airport to Iraqi authorities, a move that paves the way for Britain to withdraw from Iraq.
U.S. and Iraqi officials fear violence could flare anew ahead of provincial elections on Jan. 31 that promise to alter the delicate balance of power across Iraq.
First passenger plane
The first passenger flight from Europe in 18 years landed at Baghdad airport on Saturday, when a Swedish charter aircraft touched down.
The Nordic Leisure airliner brought in 150 people, resuming air links between Iraq and Europe for the first time since the United Nations imposed sanctions on Iraq after Saddam Hussain's 1990 invasion of Kuwait.
More international flights are expected in the next two days, including one from Hong Kong, Iraqi Transport Minister Amer Abduljabbar Ismail told reporters at the airport.
On Tuesday, Air France-KLM and Iraq's transport ministry signed a preliminary accord which will see Iraqi Airways taking off for European destinations and Baghdad airport being renovated.
In the aftermath of the 1991 Gulf War, state-owned Iraqi Airways was hit hard by U.N. sanctions imposed against Iraq and its service declined rapidly.
After the U.S.-led invasion in 2003, the airline slowly resumed flights and today the national carrier flies to the regional capitals and major cities of Amman, Beirut, Tehran, Cairo, Istanbul, Damascus and Dubai.