A suicide bomber disguised as an Iraqi policeman killed three officers and wounded 15 people on Monday, including eight US soldiers and a child, in the third such attack in over a week.
The bomber targeted a joint Iraqi and American foot patrol in Baquba northeast of Baghdad, military officials said, replicating two recent incidents in which suicide assassins were wearing security forces uniforms.
"The suicide bomber took advantage of police and he managed to reach them and blow himself up," Baquba's deputy mayor Raad al-Dahalaki said. "He looked the same as them."
An Iraqi official from the city's military operations command said three policeman had been killed and 15 people wounded, including US soldiers and a child, in the attack which happened near the mayor's office.
Neither Dahalaki nor the mayor were wounded.
Baquba is in the ethnically and religiously mixed Diyala province, considered one of the most dangerous areas in the country, where al-Qaeda in Iraq and other insurgent groups still launch regular attacks.
An American military spokesman said "eight US coalition soldiers were wounded," and that troops had come under fire from a gunman after the suicide attacker blew himself up.
"Soldiers identified a single gunman and returned fire," he said, adding that the gunman was not captured.
The attack in Baquba, northeast of Baghdad, came four days after a suicide bomber in security forces uniform blew himself up inside a heavily guarded military compound west of the capital.
There were widely varying accounts of the toll of that incident, with the defence ministry saying 38 soldiers were wounded. However, senior defence and interior ministry officials said 16 had been killed and another 50 injured.
A suicide bomber disguised in military uniform also struck inside the compound of a US-allied militia south of Baghdad on April 11, killing nine people and wounding dozens.
Iraqi Prime Minister Nuri al-Maliki warned on Sunday at a meeting of senior security officials that the danger from "terrorist cells" was far from over.
His remarks followed an upsurge in violence over recent weeks after several months in which there was a steady reduction in the number of attacks.
"We have succeeded in re-establishing security, but maintaining it is more difficult," Maliki told the meeting of senior police officers.
Also on Monday, two girls under the age of 12 were killed when a sticky bomb targeting an army officer exploded in Fallujah west of Baghdad, as he left for work, police said.
The bomb meant for Captain Saadun Mohammed Ali went off near the door of his house when he was already in his car, police Colonel Daud Maraawi said. The blast killed Ali's daughter and niece as they waved goodbye to him.
Iraq's 560,000 police and 260,000 soldiers are to assume greater responsibility for security as US forces withdraw from all cities by June 30 and from the country as a whole by the end of 2011.
Violence has plummeted over the past two years as American and Iraqi forces have allied with local tribes and former insurgents to bring calm to vast swathes of the country, but attacks remain common in some areas.
More than 80 people have been killed since the start of April, according to an AFP count based on reports from security officials.