President Hamid Karzai has returned to Afghanistan, canceling a trip to Britain after a pair of bomb attacks in Afghanistan killed at least 59 people.

Mr. Karzai arrived Wednesday in the capital Kabul to visit with some of the more than 160 wounded in the blasts. He traveled home from Germany, where he attended an international conference on Afghanistan.

Mr. Karzai said the attacks Tuesday on Ashura – the holiest day of the Shi'ite Muslim calendar – were the first of “that horrible nature” to take place on such an important religious day in Afghanistan.

The worst of the violence was in Kabul, where at least one suicide bomber detonated explosives near the Abul Fazel shrine as Shi'ite worshippers gathered. The blast killed 55 people, including women and children. The U.S. Embassy in Kabul says an American was also among the dead.

A second explosion killed four people at a shrine in the northern city of Mazar-e-Sharif, but it is not clear if Shi'ites were specifically targeted.

The Taliban denied involvement in the attacks, calling them “cruel and indiscriminate” and blaming them on the “invading enemy.”

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.

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

General John Allen, the commander of the NATO-led International Security Assistance Force in Afghanistan said the killing of Afghans by Afghans must come to an end.

Experts say the attacks, which came a day after the conference to discuss Afghanistan's future as international combat troops prepare to leave the country, underscores the importance of what was agreed in Bonn — that all countries in the region need to cooperate in securing long-term stability for Afghanistan.

The 10-day Ashura festival, which reached its peak on Tuesday, marks the death of Imam Hussein, the grandson of the Prophet Mohammad.