An al Qaeda-linked group has said it carried out the twin suicide bombings that killed 155 people in Baghdad on Sunday and revived doubts about security in the run-up to Iraq's elections in January.

The statement dated Oct. 26 was posted by the Islamic State in Iraq group on a website often used by militants to announce responsibility for such attacks.

"Suicide bombers targeted the dens of infidelity and pillars of the rejectionist Shi'ite state in the land of the caliphate," the statement said.

It employed language often used by Sunni Arab militants to describe the Shi'ite Muslim majority that has dominated the Iraqi government since the US-led invasion of 2003.

"Among the chosen targets were the ministry of oppression known as the ministry of justice and the Baghdad provincial assembly ... The enemies only understand the language of force," said the statement.

The authenticity of the claim could not be immediately verified.

The same group has said it was behind attacks near government ministries in Baghdad that killed 95 people in August.

Officials have said two mini-buses were used in Sunday's attacks, circumventing a ban on truck traffic in heavily policed central Baghdad.

Both were driven by suicide bombers from a nearby site, according to aerial images from US-operated airships that hover over the city.

The January ballot is expected to focus on security gains under Prime Minister Nuri al-Maliki after years of war and sticky questions about the distribution of power and oil wealth.

Insurgents are widely expected to try and upset an electoral process that is meant to prepare the way for an ordered withdrawal of most US troops from Iraq.