KABUL, Afghanistan - A suicide bomber struck a crowd of Shiite worshippers at a mosque in Kabul on Tuesday, killing at least 56 people and wounding 160 more in the deadliest of two attacks on a Shiite holy day -- the first major sectarian assaults since the fall of the Taliban a decade ago.
Four other Shiites were killed in the northern city of Mazar-i-Sharif when a bomb strapped to a bicycle exploded as a convoy of Afghan Shiites was driving down the road, shouting slogans for the festival known as Ashoura.
The Kabul bomber blew himself up in the midst 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. Some men were beating themselves in mourning and food was being distributed.
Photos and video from the scene show many bodies piled up on the street near the shrine, including many children.
A man who claimed to be from Lashkar-e-Jhangvi, a Pakistan-based group that has carried out attacks against Shiite Muslims, called various media outlets in Pakistan to claim responsibility for the bombing in Kabul. The validity of the claim could not be determined.
The shrine, which is near the presidential palace, was packed with worshippers and dozens more were crammed into the courtyard. Two officials from Afghanistan's National Defense Forces told CBS News the the suicide bomber approached the shrine among the worshipers. He apparently detonated his device at the entrance to the mosque. Kabul Police chief Gen Ayub Salangi confirmed that a lone suicide bomber was behind the devastating attack on the capital.
Bodies of the dead lay on top of one another where they fell to their deaths. Survivors with blood-smeared faces cried amid the chaos.
The Ministry of Interior said 55 were killed -- including two women and four children. Sayed Kabir Amiri, who is in charge of Kabul hospitals said more than 160 wounded in the blast.
That made it the single deadliest attack in the Afghan capital in more than three years. A suicide car bomber detonated his explosives at the gates of the Indian Embassy in Kabul on July 7, 2008, killing more than 60 people.
Sources tell CBS News that a third blast in Kandahar, reportedly caused by smaller explosive device, left four people injured. It wasn't immediately clear who was targeted by the blast.
Religiously motivated attacks on Shiites are rare in Afghanistan although they are common in neighboring Pakistan. No group claimed responsibility for Tuesday's blasts, reminiscent of the wave of sectarian attacks that shook Iraq during the height of the war there.
CBS News correspondent Mandy Clark reports from Kabul that officials believe the attackers deliberately picked one of the holiest days on Shiite calendar to launch the coordinated attacks. Sectarian violence is generally rare in Afghanistan, says Clark, with most of the bloodshed resulting from tribal or ethnic fighting.
Tuesday's Ashoura attacks are a worrying sign that sectarian strife could snowball in Afghanistan as foreign forces leave the country and extremist groups attempt to create more civil strife, which could enable them to operate more freely again inside the country's borders.
The Ministry of Interior in a statement blamed the Taliban and "terrorists," for the attack. It provided no other details but added that police defused another bomb that had been planted in Mazar-i-Sharif near the one that blew up.
The Taliban strongly condemned the two attacks and said in a statement to news organizations that they deeply regretted that innocent Afghans were killed and wounded.
As the sectarian attack does not generally fit the Taliban's standard anti-foreign modus operandi, suspicion fell on al Qaeda or other groups based across the border in Pakistan, where Sunni attacks on Shiites are common. Hard-line Sunnis consider Shiites nonbelievers because their customs and traditions differ from the majority sect.
CBS News' Farhan Bokhari reports that one group in particular, Lashkar-e-Jhangvi, was rapidly becoming the focus of suspicions in the region.
"The circumstantial evidence of today's attack points very very strongly towards LJ's involvement," a Pakistani security official tells Bokhari.
A Western diplomat in Islamabad concurred with the official's assessment, saying "there is enough evidence to tell us of Lashkar-e-Jhangvi's involvement. I can't get in to the specifics of intelligence information, but there were warnings floating around recently of a big attack in the pipeline, and Lashkar-e-Jhangvi was a key suspect."
Afghan President Hamid Karzai, speaking at a news conference after meeting German Chancellor Angela Merkel in Berlin, said the attack was unprecedented in scope and the first time ever that one has been carried out during a religious event.
He said it was "the first time that on such an important religious day in Afghanistan terrorism of that horrible nature is taking place."
Mohammad Bakir Shaikzada, the top Shiite cleric in Kabul, said he could not remember a similar attack having taken place on such a scale.
"This is a crime against Muslims during the holy day of Ashoura. We Muslims will never forget these attacks. It is the enemy of the Muslims who are carrying them out," he said, declining to place blame.
Shiites make up about 20 percent of Afghanistan's 30 million people, most of them ethnic Hazaras. Although thousands of Hazaras were massacred by the Taliban during fighting in the 1990s, Afghan insurgents -- nearly all of them Sunnis -- in recent years have focused their attacks primarily on U.S.-led NATO troops and Afghan security forces.
The last incident of violence between Shiites and Sunnis following the U.S. invasion 10 years ago occurred in early 2006, during Ashoura commemorations in the western city of Herat. During those riots, blamed on Islamic extremists, five people were killed and more than 50 injured.
Mahood Khan, who is in charge of the Abul Fazl shrine, said the explosion occurred just outside a courtyard where dozens of worshippers were lined up as they filed in and out of the packed building.
A few minutes after the blast, bodies could be seen loaded into the trunks of cars while wounded were led away by friends and relatives. Survivors wept in the streets.
"It was a very powerful blast," Khan said. "The food was everywhere. It was out of control. Everyone was crying, shouting. It is a disaster."
Mustafa, a shopkeeper, said he and his mother were delivering food to the worshippers when the blast occurred. Two groups of 150 to 200 people from Kabul had just prayed at the shrine and left.
Another group of more than 100 from Logar province was entering when the explosion occurred. He said the suicide bomber was at the end of the line of worshippers from Logar when he blew himself up near one of the gates to the shrine.
"It was very loud. My ears went deaf and I was blown 3 meters (yards)," said Mustafa, who uses only one name. "There was smoke and red blood on the floor of the shrine. There were people lying everywhere."
The shrine's loudspeaker continued to blast a recitation of the Quran as ambulances carried bodies and wounded away. Women stood outside the shrine wailing and holding crying children.
The shrine is close to the palace where Karzai lives and who is in Europe to attend an international conference on Afghanistan. It is named after Abul Fazl, who was an adviser to a 14th century Mogul emperor. The shrine and its blue minaret is one of Kabul's better known shrines. It is located in Murad Khane area near the Kabul river, a district that has been listed by the World Monuments Fund as one of its 100 most endangered sites of cultural heritage.