"54 civilians (were) killed and more than 100 wounded including women and children. It's not clear yet who carried out the attack. Nobody has claimed responsibility", he said, adding that the death toll may rise.

Afghanistan has a history of tension and violence between Sunnis and the Shi'ite minority, but since the fall of the Taliban, the country had been spared the largescale sectarian attacks that have troubled neighbouring Pakistan.

The noon bomb in a riverside shrine, in the heart of old Kabul, appears to set a grim new precedent.

Shortly after, a bicycle bomb exploded near the main mosque in the northern city of Mazar-i-Sharif, killing four people and injuring 17 others.

The city's streets were filled with people celebrating Ashura, but it was not immediately clear if that attack was also targetting Shi'ite worshippers.

Taliban spokesmen could not immediately be reached for comment on either attack.

The Shi'ite Muslim festival of Ashura marks the martyrdom of the Prophet Mohammad's grandson Hussein in the battle of Karbala in Iraq in the year 680.

Ashura is the biggest event in the Shi'ite Muslim calendar, when large processions are vulnerable to militant attacks, including suicide bombings. Pakistan has deployed tens of thousands of paramilitary soldiers and police during Ashura.

Blood has spilled between Pakistan's majority Sunni and minority Shi'ite militants for decades.