Attacks mainly targeting security forces in Baghdad, including two suicide car bombs minutes apart on police stations, killed at least 21 people in the capital's deadliest day in more than a month.

The violence, in which more than 70 people were wounded, showed insurgents' ability to plan and carry out coordinated attacks on well-secured targets, as Iraq weighs its options over a post-2011 American military training mission.

Two suicide attackers detonated their explosives-packed vehicles at police stations in Hurriyah in north Baghdad, and Alwiyah in the centre, at about 8:30 am (0530 GMT), killing at least 17, interior and defence ministry officials said.

"I saw the bomber trying to pass the barriers, but he blew up his vehicle. The concrete T-walls collapsed and I fell on the ground," said Ali, a policeman at the Alwiyah station who only gave his first name.

He said he was not injured thanks to the walls, but that his colleagues who had been standing at the gate of the station had been torn apart.

Human remains and shrapnel from the bomb were scattered for about 100 metres (yards) from the site of the explosion, and security forces cordoned off the scene, according to an AFP correspondent.

Parliament speaker Osama al-Nujaifi condemned the attacks in a statement released by his office.

"These attacks are a challenge against Iraq and the political process, because the terrorists want to confirm that they exist here just before the departure of US soldiers," said Baghdad provincial council member Mohammed al-Rubaie, who was at the scene of the Alwiyah explosion.

An interior ministry official put the toll from that attack at 13 dead and 25 wounded, while a defence ministry official said 15 people were killed and 25 injured.

Rubaie said seven of the wounded were policemen, including one woman. The bomber tried to enter the Alwiyah station but was blocked by concrete walls, he said.

Both officials, who spoke on condition of anonymity, said four people were killed in the Hurriyah blast, and at least 22 people wounded.

Differing tolls are common in the confusion that follows major attacks in Iraq.

The attack seriously damaged the police station in Alwiyah and created a crater in the street about four metres (yards) wide and two metres deep. It also damaged a nearby primary school.

The street in front of the police station had been closed from 2004, but was reopened about a month ago to ease the flow of traffic, Rubaie said.

Another car bomb killed three people and wounded 11, including police, at Al-Ilam in southwest Baghdad on Wednesday, defence and interior ministry officials said.

Baghdad's Yarmuk hospital received six wounded from the explosion in Al-Ilam, among them a police major, a medical source said.

A car bomb in Hurriyah killed one civilian and wounded an Iraqi army brigadier, nine of his bodyguards and two civilians, according to the officials.

The defence ministry official said the brigadier general was seriously wounded.

In other attacks, a magnetic "sticky bomb" wounded a police brigadier general in Al-Sulaykh in north Baghdad, while two police were wounded by shots from a silenced pistol in the Jihad neighbourhood in south Baghdad, said the interior ministry official.

Wednesday's attacks come with less than three months to go before a year-end withdrawal deadline for the roughly 41,500 US soldiers currently in Iraq, with Baghdad and Washington yet to reach any accord on a post-2011 training mission.

The apparently coordinated attacks were the deadliest to hit the capital since August 28, when a suicide attack blamed on Al-Qaeda at Baghdad's biggest Sunni mosque killed 28 people, including an MP.

Despite a decline in violence nationwide since its peak in 2006 and 2007, attacks remain common. A total of 185 Iraqis were killed in violence in September, according to official figures.