Afghan President Karzai cancels UK trip after bombings
The twin attacks apparently targeting Shia Muslims killed at least 58 people.
A suicide bomb struck a Kabul shrine, killing at least 54, while the other blast struck near a Shia mosque in Mazar-i-Sharif at about the same time.
The attacks seemed to be sectarian, raising fears of new violence.
Mr Karzai was in Germany on Tuesday evening after attending the international conference on his country in Bonn, and was later due to travel to the UK for talks with UK Prime Minister David Cameron on Wednesday.
He said earlier it was "the first time that on such an important religious day in Afghanistan terrorism of that horrible nature is taking place".
The blasts coincided with the Shia Muslim festival of Ashura - the most important day in the Shia calendar which is marked with a public holiday in Afghanistan.
Ashura is the climax of Muharram, the month of mourning for the martyrdom of the Prophet Muhammad's grandson.
Though tensions exist between Afghanistan's Sunni and minority Shia Muslims, most attacks in Afghanistan in recent years have targeted government officials or international forces, correspondents say; Kazinform cites BBC.
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