Afghan officials say at least 30 people have been killed in a suicide bomb attack on a Shi'ite shrine in central Kabul.

Officials say the suicide bomber detonated his explosives near the Abul Fazel shrine as pilgrims gathered Tuesday to celebrate the Shi'ite festival of Ashura.

Meanwhile, officials say a second explosion targeted a mosque in the northern city of Mazar-e-Sharif on Tuesday, killing four people. It is not clear whether Shi'ites were also the target of the second attack.

No one has immediately claimed responsibility for either attack.

The 10-day Ashura festival, which reaches its peak on Tuesday, is the most significant holiday for Shi'ite Muslims. It marks the martyrdom of Hussein, the grandson of the Prophet Muhammad.

Attacks between Afghanistan's Sunni citizens and minority Shi'ite population have been rare in recent years. Attacks between the two groups are more frequent in neighboring Pakistan.

The attacks come a day after world leaders gathered in the German city of Bonn to discuss Afghanistan's future as international combat troops prepare to leave the country.

Afghan President Hamid Karzai told the conference that after the withdrawal of NATO troops from his country in 2014, Afghanistan will still need international help for at least another decade.

Pakistan, considered vital to any prospect of stability in Afghanistan, boycotted the one-day meeting in response to a cross-border attack by NATO late last month that killed 24 Pakistani soldiers.