More than 40 Iraqis were killed today in separate bomb attacks aimed at bringing chaos to the holiest festival in the Shia Muslim calendar.

As millions of Shias took to the streets across the Islamic world to mark the climax of Ashoura, which commemorates the death of the grandson of the Prophet Muhammad, bombers attacked at least two ceremonies in northeastern Iraq. A gunman killed four pilgrims at a separate festival in southern Baghdad.

The deadliest explosion, in the town of Mandali, 60km north east of Baghdad and near the border with Iran, claimed the lives of 23 worshippers at a Shia mosque, doctors said. A further 60 people were injured when a suicide bomber detonated a belt of explosives in the midst of a crowd of around 150 people entering the Ali al-Akbar mosque at about 12.20pm, police said.

The blast was the second major attack of the day in Diyali, a province in northern Iraq that has suffered months of sectarian violence among its mixed Sunni and Shia population. About an hour earlier, explosives left in a rubbish bin killed 13 people in the town of Khanaqin, also near the border with Iran.

Around 40 people were wounded when the bomb went off among Shias gathered in the street in central Khanaqin, a mainly Sunni Kurdish town with a small Shia community. Four people were then killed and six injured when a gunman ambushed worshippers in Bayaa, a district in southwestern Baghdad.

The climax of Ashoura, a week-long festival which ends today, sends devout Shias to mosques and other public places to flagellate and cut themselves with knivesin a display of mourning for the death of Imam Hussein, the grandson of Muhammad, who was killed by the army of the Yazid caliphate in 680AD.

The festival has been the source of enormous tension and violence between Iraq’s Sunni and Shia populations because the death of Imam Hussein, at the hands of Sunnis, is traditionally regarded as the cause of the schism between the two great strains of Islam. What’s more, he was killed on the Karbala plain, in central Iraq.

In 2004 and 2005, synchronised explosions and mortar attacks aimed at disrupting Ashoura killed more than 300 worshippers at shrines in Karbala and Baghdad. Yesterday Iraqi police and government officials claimed to have broken up an extremist Shia sect that was intent on murdering clerics in the holy city of Najaf today. A total of 263 militants were killed and 392 arrested after a huge battle on the outskirts of Najaf on Sunday. A further 11,000 police were deployed to protect worshippers in Karbala.

Processions and gatherings to mark Ashoura took place across the Islamic world today. In Lebanon, Hezbollah, the Shia Islamist movement, used the occasion to hold an enormous rally in southern Beirut and berate Israel and the western-backed government of Prime Minister Fouad Siniora.

Hassan Nasrallah, the leader of Hezbollah, accused America and Israel of trying to turn Muslims against each other and starting civil wars in Lebanon, Iraq and the Palestinian territories, which are all torn by sectarian and factional differences.

“The future of Israel is death and the future of this umma (Islamic nation) is life,” he said, as hundreds of Hezbollah members gathered to beat their chests in time and walk through the rainy streets of Beirut. Women raised their fists and joined them, shouting Shia cries of: “At your service, O, Hussein!”