|Iraqi security forces have borne the brunt of attacks by anti-government fighters in recent months [AFP]
Iraqi officials say at least six people have been killed and 35 others wounded in two separate attacks in Baghdad.
In the first of Wednesday's two attacks, three policemen and one civilian were killed when a parked car bomb exploded near a bus station in Baghdad's southern Bayaa neighbourhood.
A second bomb targeting police and rescue services arriving at the blast site detonated minutes later.
There were no reports on casualties from the second blast.
In the second attack, which occurred in the Sheikh Omar neighbourhood of eastern Baghdad, two bombs near a bus station went off simultaneously, killing two civilians and wounding 12 others.
Health officials confirmed the death toll of the Sheikh Omar blast.
The bombs appeared to target a police patrol, the sources said, and Iraqi police and soldiers were among the dead and wounded.
The attack came a day after an Iraqi soldier reportedly fired a barrage of bullets at US troops protecting one of their commanders during a visit to an Iraqi army base and killed two of them.
Nine Americans were wounded in Tuesday's shooting.
The Americans attacked were providing security for a commander attending a meeting with Iraqi military personnel at a base near the city of Tuz Khormato, about 210km north of Baghdad.
Major-General Mohammed al-Askari, an Iraqi defence ministry spokesman, said Iraqi and US troops had been playing a sports match when a quarrel erupted between one local and one US soldier.
"The Iraqi soldier opened fire on them," he said, naming the assailant as Soran Rahman Saleh Wali.
"The American soldiers killed the Iraqi soldier. We have opened a high-level investigation into this issue."
The assailant opened fire after an argument and was killed in the shootout that followed, Colonel Hussein Rashid, Tuz Khormato's police chief, said.
He did not provide details on the nature of the argument.
The US military said in a statement: "Eleven US soldiers were engaged with small arms fire, killing two and wounding nine, inside an Iraqi army commando compound."
Al Jazeera's Rawya Rageh, reporting from Baghdad, said: "These are the first US military fatalities to be reported since the change of command ceremony on September 1 that marked the end of 'Operation Iraqi Freedom' and the beginning of 'Operation New Dawn'."
"We have not heard of an attack of this magnitude on US soldiers in quite a while."
Source: Al Jazeera and gencies