Kabul, Afghanistan (CNN) -- Afghan President Hamid Karzai has canceled a visit to the UK to return home following Tuesday's deadly blasts in the capital, Kabul, and in the northern city of Mazar-e Sharif.
A spokesman for the Afghan embassy in London said Karzai had been due in London late Tuesday from Germany but was flying back to Afghanistan after the twin suicide attacks killed 60 people and wounded scores of others in the two cities.
A suicide bomber detonated a device at a Shiite shrine in Kabul, as worshippers were marking the Shiite holy day of Ashura, Afghan Health Ministry spokesman Kargar Norughli said. Fifty-six people were killed and 193 were wounded, Norughli added.
Four people were killed in an explosion at a roundabout on a busy street in Mazar-e Sharif, the provincial capital of Afghanistan's northern Balkh province, police official Lal Mohammad Ahmadzai said. Another 21 were wounded in that attack.
"The enemies tried to spread fear in this important holiday in the city," Ahmadzai said.
It was not immediately clear whether the attack in Mazar-e Sharif was linked to the attack in Kabul.
The Taliban denied involvement in Tuesday's attacks.
A Sunni group in Pakistan with a history of sectarian attacks against Shiites apparently claimed responsibility for the attack at the shrine, but it was not immediately clear whether the claim was vaild.
A man identifying himself as a spokesman for Lashkar-e-Janghvi al Almi, a group with links to al Qaeda and the Pakistan Taliban, made the claim in a call to Radio Mashaal, a Pashto-language station in Pakistan sponsored by the U.S. government.
The group is an offshoot of the powerful Lashkar-e-Janghvi (LeJ), which has a record of high-profile suicide bombings in Pakistan, including the attack on the Marriott Hotel in Islamabad in 2008.
Haji Mohammad Mohaqiq, a leading Shiite member of Parliament, blamed "foreign criminals."
The attacks showed "that those who claim to be defenders of Islam" are liars, and showed "how far from humanity they are," he said.
The attackers committed "these crimes for the interest of those foreigners who are controlling them so that they could create hatred among Muslims in Afghanistan," he said.
In Iraq, where large-scale sectarian attacks have occurred frequently, government officials and analysts have said the goal of extremists was to foment sectarian tensions.
The U.S. Embassy in Afghanistan issued a statement Tuesday condemning the "the twin suicide bombings that killed dozens of worshippers, many of them women and children."
The bombs detonated nearly simultaneously, the statement said.
Afghanistan has seen previous attacks on mosques. In 2006, rioting broke out between Shiites and Sunnis at an Ashura festival in Herat, leading to several deaths. But the country has not seen sectarian attacks of the scale that occurred Tuesday.
The attacks came a day after an international conference in Bonn, Germany, addressed the state of affairs in Afghanistan, and Afghan officials pushed for international support and contributions.
The U.S. Embassy statement Tuesday vowed that the United States "remains undeterred in standing with the Afghan people against the scourge of terrorism in our mutual aim of promoting peace and prosperity."
Gen. John Allen, commander of NATO's International Security Assistance Force, said the attack on the Ashura pilgrims "on one of the holiest of days in the Islamic calendar is an attack against Islam itself, and we denounce and condemn these atrocities in the strongest of terms.
"Our prayers and deepest sympathies are with the families and loved ones of those innocent civilians killed or injured in today's horrific attacks," Allen said.
Ambassador Simon Gass, NATO's senior civilian representative in Afghanistan, called the attacks "horrifying."
"That men, women and children are killed and injured on Ashura is particularly tragic," he said.
Ashura commemorates the martyrdom of Hussein, grandson of the Prophet Mohammed. Hussein's death in battle in Karbala, Iraq, in 680, is one of the events that helped create the schism between Sunnis and Shiites, the two main Muslim religious movements. Shiites are a minority presence in Afghanistan, which is predominantly Sunni.
At the Bonn conference on Monday, Afghan President Hamid Karzai warned that the Taliban could make a comeback as the country struggles with security, a decade after a U.S.-led coalition ousted the hard-line militia from power.
"If we lose this fight, we are threatened with a return to a situation like that before September 11, 2001," Karzai said.
In an e-mailed statement to journalists, Taliban spokesman Zabiullah Mujahid condemned Tuesday's attacks. He accused NATO forces of playing a role in the attacks "to sow mistrust and hatred among Muslims so they can stay longer."
Karzai, at Monday's conference, said that though there had been progress over the past 10 years, stability remains a distant goal.
"Our shared goal of a stable, self-reliant Afghanistan is far from being achieved," he said.
CNN's Tim Lister, Mohammed Tawfeeq, and Josh Levs contributed to this report.