BAGHDAD (Reuters) - Bombs killed nearly 40 people in Iraq on Thursday, including 20 at a tribal council meeting in Anbar province just days before the U.S. military transfers control of security for the vast western region to Iraqi forces.

U.S. SSG. Don Roggers, 37, from New Jersey, of 1/8 Infantry Battalion, stands guard next to a room where U.S. and Iraqi military officials are holding a meeting to discuss security, future projects and the relationship between the Iraqi army and residents, at a joint U.S. and Iraqi army military base in Mosul June 25, 2008. REUTERS/Eduardo Munoz

The U.S. military said there were American troop casualties in the attack in Anbar but gave no details.

In the northern city of Mosul, a car bomb on a crowded street killed 18 people and wounded 80 near the office of the governor of surrounding Nineveh province, U.S. forces said.

Nineveh Governor Duraid Kashmula had just left his office to investigate damage caused by two rocket-propelled grenades when the car bomb went off. The governor was unhurt. Officials said the bomb may have been an assassination attempt.

Dramatic television pictures showed the bomb exploding near an old woman on the side of a street. A hail of gunfire burst out as security guards opened fire.

Violence in Iraq fell to a four-year low last month, but there has been a spate of attacks in the past week, especially in and around Mosul, which the U.S. military has called Sunni Islamist al Qaeda’s last major urban stronghold in Iraq.

The attacks suggest al Qaeda, significantly weakened after a wave of U.S. offensives in the past year, is not a spent force. A U.S. military spokesman said the Mosul attack fitted a pattern of al Qaeda attacking Iraqis and Iraqi security forces.

The American military said al Qaeda was likely behind the suicide bombing against U.S.-backed Sunni Arab tribal leaders in the Anbar town of Garma, 30 km (20 miles) northwest of Baghdad.

A police spokesman in the nearby city of Falluja said 20 people had been killed and 12 wounded.

A tribal leader, Mizher Mshawih, and the head of the district council, Kamal Abdul-Salam, were among those killed, he said, as well as three policemen.

Anbar was once the heartland of the Sunni Arab insurgency against U.S. forces and an al Qaeda haven.

In late 2006, Sunni Arab tribal leaders, sick of al Qaeda’s indiscriminate killing of civilians and harsh interpretation of Islam, joined with the U.S. military to expel the group. Many al Qaeda fighters fled north, to provinces such as Nineveh.

Violence in Anbar has fallen so sharply that the province is scheduled to become the first Sunni Arab province to be transferred to Iraqi security control on Saturday.

It will be the 10th of Iraq’s 18 provinces to revert to Iraqi control. The previous nine have been Kurdish or Shi’ite.

ANBAR HANDOVER CEREMONY STILL ON

A U.S. military source in Anbar who declined to be identified said there were no immediate plans to postpone the handover date in response to the bombing.

“We still have people planning for the event. Obviously our senior commanders are always assessing, but as of right now, there is no change,” he said.

The suicide bomber managed to get into a meeting between tribal leaders and Abdul-Salam, the district council chief. The meeting was being held in the local council building.

Defence Ministry spokesman Major-General Mohammed al-Askari blamed al Qaeda for the surge of attacks in Mosul.

“These are sleeper cells that seize any opportunity ... There will be quick measures to end these attacks,” Askari said, without elaborating.

Iraqi security forces stepped up a crackdown against al Qaeda last month in Mosul, Iraq’s third largest city.

Militants have increasingly targeted Iraqi councils.

On Tuesday, a bomb killed 10 people, including two U.S. government employees and two U.S. soldiers, at a council meeting in the Baghdad stronghold of Shi’ite cleric Moqtada al-Sadr.

On Monday, a gunman killed two U.S. soldiers and wounded three as they left a council meeting southeast of Baghdad.

U.S. forces said an American soldier was killed in eastern Baghdad on Wednesday by an armour-piercing roadside bomb.

It brought to eight the number of American troops killed in Iraq this week and the number killed in June to 26.

That is up from 19 American soldiers killed in May, the lowest monthly total since the 2003 invasion. More than 4,100 U.S. troops have been killed in Iraq.