A suicide bomber attacked a Shia Muslim shrine in central Kabul today where a crowd of hundreds had gathered for the festival of Ashura, killing at least 55 people and injuring hundreds more.
"This is the first time on such an important religious day in Afghanistan that terrorism of that horrible nature is taking place," Afghan President Hamid Karzai told journalists in Germany, where the conference on Afghanistan's future was held.
The city's streets were filled with people celebrating Ashura, but it was not immediately clear if that attack was also targeting Shia worshippers.
The Taliban condemned the bomb attacks as the brutal work of "enemies", a spokesman for the insurgent group said.
"The Islamic Emirate strongly condemns such a cruel, indiscriminate and un-Islamic attack," the statement added, using the name by which insurgent group refers to itself.
Shortly afterward, a bicycle bomb exploded near the main mosque in the northern city of Mazar-i-Sharif, killing four people and injuring 17 others.
Afghanistan has a history of tension and violence between Sunnis and the Shia minority, but since the fall of the Taliban the country had been spared the large scale sectarian attacks that have troubled neighbouring Pakistan.
The Shia 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 Shia 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.
Sectarian strife has intensified since Sunni militants deepened ties with al-Qaeda and Pakistani Taliban insurgents after Pakistan joined the US-led campaign against militancy after the September 11th attacks.