Twin blasts in Afghanistan marred the Shi'ite holy day of Ashura Tuesday, killing nearly 60 people – mostly Shi'ite Muslims – in the central and northern parts of the country.

The worst of the violence struck the capital Kabul, when at least one attacker detonated explosives near the Abul Fazel shrine as pilgrims gathered. It was the deadliest bombing in the capital since 2008, killing 55 people and wounding 160 others.

Eyewitnesses say that some hospitals in the area became overwhelmed with the number of wounded.

Meanwhile, a second explosion targeted a shrine in the northern city of Mazar-e-Sharif, killing four people. It is not clear whether Shi'ites were the specific target.

The Taliban released a statement on Tuesday saying it did not plan the attacks, calling them “cruel and indiscriminate” and blaming them on the “invading enemy.”

However, the Pakistan-based insurgent group Lashkar-e-Jhangvi al-Alami claimed responsibility for the Kabul attack. The Sunni extremist group is an offshoot of the bigger Lashkar-e-Jhangvi , which is affiliated with al-Qaida and is responsible for a number of attacks against Shi'ites in Pakistan.

LeJ maintained training camps in Afghanistan during Taliban rule, but has not mounted attacks recently outside of Pakistan.

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

Afghan President Hamid Karzai immediately condemned the bombing, saying it was the first time a terrorist attack has taken place on “such an important religious day in Afghanistan.”

U.S. President Barack Obama also strongly condemned the violence, saying the United States continues to stand with the people of Afghanistan against terrorism.

The attacks also 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.

President Karzai told the conference that after the withdrawal of NATO troops from his country in 2014, Afghanistan still will 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.