A spate of bomb attacks in and around Baghdad, the deadliest of which targeted Shiite areas in the capital, killed at least 12 people on Tuesday, officials said.

The violence comes amid a political standoff in Iraq pitting the Shiite-led government against the main Sunni-backed political bloc, stoking sectarian tensions barely a month after US troops completed their withdrawal.

In the deadliest attack, two bombs exploded within half an hour of each other in the capital's Sadr City Shiite bastion, killing six people and wounding 32, an interior ministry official said.

The first bomb ripped through a group of workers at around 6:45 am (0345 GMT) while the second exploded outside a bakery. Among the wounded were two women and a child.

Two car bombs in north Baghdad targeted secondary schools, with one exploding in the northwestern Shula district, killing two people and wounding 16, and another killing one person and wounded 13 in the Al-Hurriya neighbourhood, the official added.

The bombings are the latest in a spate of attacks against Shiites, which have risen since US forces completed their withdrawal from Iraq on December 18.

Also on Tuesday, three roadside bombs struck in front of neighbouring houses of two policemen in Abu Ghraib, on Baghdad's western outskirts. Three civilians, including a woman, were killed, according to a security official and Dr Omar Dalli at nearby Fallujah hospital.

Though violence in Iraq is down markedly from its peak during 2006 and 2007, attacks are still common, and more than 200 people, mostly Shiite pilgrims, have been killed since the US drawdown.

The troop pullout coincided with a political crisis in Iraq, pitting the Shiite-led government against the main Sunni-backed bloc which accuses Prime Minister Nuri al-Maliki of centralising power.

Iraq on Sunday claimed that Turkey, Iran and unnamed Arab countries were trying to "intervene" in Baghdad's month-long crisis and not respecting its sovereignty.

Reflecting the ongoing sectarian tensions, the Honein jihadist forum posted a message on Monday vowing further attacks against Iraqi Shiites.

"The violent attacks against the Rawafid (the name used for Shiites by Sunni extremists) will continue," Al-Qaeda front group the Islamic State of Iraq said in a statement, while claiming responsibility for attacks on Shiite pilgrims over the past month.

"The lions of the Islamic State of Iraq (will not cease their operations)... as long as the Safavid government continues its war. We will spill rivers of their blood as reciprocity."

The jihadists often invoke Iran's Safavid past, referring to the Shiite dynasty that ruled Persia between the 16th and 18th centuries, and conquered part of Iraq, when denouncing the Baghdad government, which they say is controlled by Tehran.