Afghan officials say an explosion has rocked a Shi'ite Muslim mosque in central Kabul, causing an unknown number of casualties.

Officials say the explosion happened as pilgrims were gathered to celebrate the Shi'ite holiday of Ashura on Tuesday.

It is unknown if the exposion was caused by a suicide bomber or if the bomb was planted inside the mosque.

Meanwhile, officials say a bicycle bomb killed at least four people in the northern city of Mazar-e-Sharif on Tuesday.

No other details were immediately available.