At least 55 people were killed after a suicide bomber detonated an explosive device inside a mosque in Kabul, the single deadliest attack in the Afghan capital in more than three years.

The bomber blew himself up while in the middle of a crowd of men, women, and children gathered outside the Abul Fazl shrine to commemorate the seventh century death of the Prophet Muhammad's grandson, Imam Hussein.

In a second attack, four people died when a bomb strapped to a motorcycle exploded during a convoy. Twenty-one people were also wounded.

Afghan President Hamid Karzai, speaking at a news conference in Berlin, said the attack was "the first time that on such an important religious day in Afghanistan terrorism of that horrible nature is taking place."

No group claimed responsibility for Tuesday's bombings, however Sunni Muslims often target Shiites during their religious observations.

Religious attacks in Afghanistan are rare. The Afghan government and the Taliban strongly condemned the two attacks.

Meanwhile in Iraq, a bomber attacked a Shiite neighborhood in Baghdad, killing at least eight people and injuring more than 20.