Iraqi security forces secure the scene of a car bomb attack at a Shi'a political organisation's rally in Baghdad. REUTERS/Thaier al-Sudani

Baghdad - A series of explosions killed 28 people and wounded more than 40 at a Shi’a political organisation's rally in Iraq on Friday, police and medical sources said.

The militant group, Asaib Ahl Haq (League of the Righteous), was presenting its candidates for elections on April 30 at the rally in eastern Baghdad. Three bombs exploded in succession as people were leaving, Reuters reporters at the scene said.

A roadside bomb blew up near the main gate, followed by a suicide car bomb after a few minutes and then a final explosion.

A Twitter account, associated with the Al Qaeda offshoot called the Islamic State of Iraq and the Levant (ISIL), rejoiced at the attack but did not claim it.

“A knight from the state of Islamic knights has detonated his explosive vest near the Asaib podium while they were parading... killing dozens including commanders,” it said.

The attack came as tensions ran high in Iraq before its national election and the Iraqi security forces locked in a four-month battle with ISIL in western Anbar province.

It appeared to be the work of ISIL aimed at baiting the group to strike Sunni neighbourhoods or communities in hopes of provoking a full-fledged civil war.

Asaib's main leader Sheik Qais Khazaali had just delivered a speech accusing some politicians of aiding terrorism and vowed his movement was ready for any action by ISIL.

“To all ISIL..., we are ready. We are prepared,” he said. “We are the defenders of this country. You will never reach us.”

He added: “If ISIL is the sickness, were are the medicine.”

As people started to leave the stadium, the first bomb exploded. Grey smoke rose in the air and people ran or scrambled for cover. The a white mini-van raced to the stadium's main gate and detonated, unleashing a massive ball of fire.

Army and police shot in the air and a final explosion shook the ground. Asaib members commandeered cars to rush the injured to hospital. A wounded man limped away, stained in blood, while people hunted for missing friends or relatives.

Asaib, which has formed its own party, al-Sadiqoon (the truth seekers), is accused by some Sunnis and Shiites of carrying out killings and driving families from their homes.

Khazaali denies the allegations but says his movement defends Iraq against terrorism. Some of Asaib's members are in Syria defending the shrine of Sayyida Zainab in Damascus.

Pictures of its slain fighters from Syria can be seen around Baghdad and Shi’a cities across the south.

Khazaali was an aide to Shi’a cleric Muqtada Sadr and led his own faction of fighters, who broke away from Sadr's Mahdi Army militia. At the height of sectarian violence in 2006 and 2007, some of the worst attacks on Sunnis were blamed on Asaib.

The group also carried out attacks on the US military.