* Three bombs explode at stadium
* Islamic State of Iraq and the Levant claims responsibility
* Shi'ite leader's speech denounced Sunni radicals (Adds claim of responsibility)
By Raheem Salman
BAGHDAD, April 25 (Reuters) - A series of explosions killed 28 people and wounded more than 40 at a Shi'ite 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 went off near the main gate, followed by a suicide car bomb after a few minutes and then a final explosion.
Al Qaeda offshoot the Islamic State of Iraq and the Levant (ISIL) claimed responsibility for the attack in a statement posted on the Internet.
The group said it had carried out the bombings in response to "murder, torture and displacement" of Sunnis by Shi'ite militias which "massacred children and women".
The attack came as tensions ran high in Iraq in the runup to a national election on April 30 and as the Iraqi security forces are 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.
SPEECH AGAINST SUNNI RADICALS
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'ite cities across the south.
Khazaali was an aide to Shiite 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 U.S. military. (Reporting by Raheem Salman; Editing by Ned Parker and Andrew Roche)