The U.S. ambassador in Afghanistan said Saturday that the United States has virtually no information about the motive or culprit behind a rare suicide bombing that killed scores of Shiite worshipers earlier in the week, but he asserted that it was unlikely to spawn sectarian violence.

Ambassador Ryan Crocker said he was skeptical of reports that a hard-line Pakistani militant group that has claimed it carried out Tuesday’s attack has a nascent Afghan offshoot. The prospect has worried Afghans, who fear it could change the dynamics of the Afghan war by exacerbating ethnic and sectarian tensions.

“I very much doubt that there is such a thing,” Crocker told reporters in Kabul on Saturday morning. “I do not see this turning into sectarian violence.”

The attack outside the Abul Fazal Abbas shrine in Kabul during Ashura, the holiest day in the Shiite Muslim calendar, sparked outrage among ethnic Hazaras, most of whom are Shiite. So far, the anger appears to be directed mainly toward Pakistan, which prominent Hazaras and Afghan officials accuse of tolerating, and in some cases supporting, attacks in Afghanistan.

Mohammad Mohaqiq, a member of parliament who is among the country’s most influential Hazaras, said Afghans would not be reeled into a cycle of sectarian violence, even if attacks against Shiite civilians were to become commonplace.

“Even if 100 of these attacks happened, they would not break the morale of the people,” he said Saturday. “There is no tension here between Sunnis and Shiites.”

Mohaqiq said Pakistan’s intelligence service was probably behind the attack.

“They want to move the fighting from Pakistan to Afghanistan,” he said.

News outlets in Pakistan have said that Lashkar-i-Jhangvi, a militant group with ties to al-Qaeda and the Taliban, claimed to have ordered the attack. The BBC reported Saturday that a man who identified himself as a commander of the group had said in an interview that the bombing was carried out by a new Afghan wing.

The man, identified as Ali Sher-e-Khuda, said the attack was an attempt to fight discrimination by “Afghanistan’s ruling Shiite elite.” Ethnic Pashtuns, who make up the majority of the country’s population, are Sunni.

Afghan officials and some Pakistani journalists expressed doubts about the man’s account.

Pakistani officials have said they do not support Lashkar-i-Jhangvi, adding that they have cracked down on the group. They noted that no attacks targeting Shiites were carried out in Pakistan on Tuesday, the day of the Kabul attack.

The bombing, which killed at least 56 civilians, was particularly jarring because insurgent groups that have been battling NATO and Afghan forces here have seldom carried out large-scale attacks that did not include a military target. If Lashkar-i-Jhangvi did it, Crocker said, that would be surprising for a group that commanders in Afghanistan had not previously deemed a threat.

“They have not been on the screen for years,” said Crocker, a veteran diplomat who has also served in Islamabad. U.S. officials have been quick to blame Pakistan-based insurgent groups for large attacks in Kabul. But Crocker said they know next to nothing about who was behind Tuesday’s bombing. “Your speculation would be as good as mine,” he said.

Mohammed Qadir Yurad, 41, a Hazara resident of Kabul, said Tuesday’s attack would not trigger the type of ethnic tension that fueled a civil war in the 1990s.

“Over 30 years of war have passed,” he said. “They have helped Sunnis and Shiites work together.”

Special correspondent Javed Hamdard contributed to this report.