The New York Times reports: A Pakistan-based extremist group claimed responsibility for a series of coordinated bombings aimed at Afghan Shiites on Tuesday, in what many feared was an attempt to further destabilize Afghanistan by adding a new dimension of strife to a country that, though battered by a decade of war, has been free of sectarian conflict.

The attacks, among the war’s deadliest, struck three Afghan cities — Kabul, Kandahar and Mazar-i-Sharif — almost simultaneously and killed at least 63 Shiite worshipers on Ashura, which marks the death of Shiite Islam’s holiest martyr.

One of the dead in Kabul was an American man, according to the Public Health Ministry. The American Embassy confirmed that there had been an American fatality but declined to identify the victim.

Targeted strikes by Sunnis against the minority Shiites are alien to Afghanistan. So it was no surprise to Afghans when responsibility was claimed by a Sunni extremist group from Pakistan, where Sunnis and Shiites have been energetically killing one another for decades.

The group, Lashkar-e-Jhangvi, had not previously claimed or carried out attacks in Afghanistan, however, and its emergence fueled suspicions that Al Qaeda, the Taliban or Pakistan’s spy agency — or some combination of those three — had teamed up with the group to send the message that Afghanistan’s future stability remained deeply tenuous and indeed dependent on the cooperation of outside forces.

“Never in our history have there been such cruel attacks on religious observances,” said President Hamid Karzai, in a statement released by his office. “The enemies of Afghanistan do not want us to live under one roof with peace and harmony.”

The timing of the attacks was especially pointed, coming a day after an international conference on Afghanistan in Bonn, Germany, that had been viewed as an opportunity for Afghanistan to cement long-term support from the West.