At least 18 people have been killed in car bomb attacks on police stations north of Baghdad, Iraqi police say.
A vehicle packed with explosives rammed one of the police stations
The blasts happened minutes apart about 0800 local time (0500GMT) in the towns of Khan Bani Saad and Baquba.
The area is known as a stronghold for supporters of ousted Iraqi leader Saddam Hussein.
US military officials are investigating whether a civilian cargo plane forced to make an emergency landing at Baghdad airport was hit by a missile.
"A DHL plane took off from Baghdad airport this morning and was hit by a SAM-7 surface to air missile," an unidentified military official was quoted by French news agency AFP as saying.
A BBC correspondent in Baghdad, Peter Biles, says if this was the case, it would be the first time a civilian aircraft has actually been hit, although guerrillas have often tried to attack planes at Baghdad airport since the end of the war in May.
MAJOR POST-WAR ATTACKS
12 November: 26 die in suicide attack on Italian police base in Nasiriya
2 November: 16 US soldiers die as Chinook helicopter downed
27 Oct: Red Cross and other buildings in Baghdad bombed, more than 30 killed
12 Oct: Baghdad Hotel bombed, six dead
9 Oct: Police station in Baghdad bombed, 10 killed
29 Aug: Mosque near Najaf bombed, dozens dead including Shia Islam's top cleric in Iraq
19 Aug: UN headquarters in Baghdad bombed, 23 killed including head of mission
7 Aug: Jordanian Embassy bombed, 14 killed
The aircraft, an Airbus A300 cargo plane with three crew members on board, declared an "in-flight emergency", US military spokesman Lieutenant Colonel Byron James said.
Witnesses reported seeing the plane trailing thick, black smoke, with one of its wings on fire.
The plane was heading from Baghdad to Bahrain when it was forced to turn back.
A spokeswoman for the German-owned DHL courier firm said all those on board escaped injury.
DHL has suspended flights to Baghdad for the time being.
Six Iraqi policemen and three civilians were killed when a car packed with explosives rammed into the police station at Khan Bani Saad 50 kilometres (30 miles) north-east of Baghdad, US military sources said.
"A Chevrolet car came very fast at the station. Police opened fire but it didn't stop," said police chief Ismail Kano al-Askari.
The blast left a large hole in the wall of the building, an AFP journalist reported at the scene.
The local hospital was overwhelmed by the casualties.
"We received so many body parts it's difficult to know how many died," said doctor Taleb Hussein al-Tamimi.
About 15 kilometres north, a second car bomb rocked the main police station at Baquba, killing seven policemen and two civilians, a US mlitary spokesman said.
The hospital in Baquba was already treating casualties from the attack in Khan Bani Saad when victims from the second bombing started coming in.
The towns lie in the so-called "Sunni triangle" area - a stronghold of supporters of Saddam Hussein and scene frequent attacks against US forces by insurgents.
The attacks came a day after US Ambassador to the United Nations, John Negroponte, told the Security Council the security situation in Iraq remained a "major preoccupation" for the US.
Mr Negroponte urged more nations to come forward and offer troops to the multinational force operating in Iraq.