The United States on Wednesday urged greater action by Pakistan against a Sunni Muslim militant group that Afghanistan blamed for an unprecedented massacre against its Shiite minority.
Afghan President Hamid Karzai said that the banned Pakistani extremist movement Lashkar-e-Jhangvi orchestrated the bloodshed Tuesday on the holy day of Ashura.
Fifty-five people were killed in Kabul and another four in a similar attack in the northern city of Mazar-i-Sharif.
State Department spokesman Mark Toner said the United States did not know the full details of the attacks but that Secretary of State Hillary Clinton had Lashkar-e-Jhangvi in mind when she urged Pakistan to act against extremists during an October visit to Islamabad.
"It's precisely the kind of organization that the Secretary was trying to address when she went to Pakistan in calling for Pakistan to do more to combat this kind of extremist terrorist activity within its own borders," Toner told reporters.
Pointing out that Lashkar-e-Jhangvi has been blamed for attacks in Pakistan as well, Toner said: "It's clearly a threat to both countries."
"It's just too important, the threat we face. There needs to be ongoing, sustained and even increased cooperation and coordination between Afghanistan (and) Pakistan and certainly with the international community," Toner said.
Toner also confirmed that one US citizen was among the dead in Kabul. He said that the American was a civilian and not linked to the US government but declined further details, saying the family had requested privacy.
Karzai on Wednesday vowed to press Pakistan to take action against the Lashkar-e-Jhangvi, potentially raising fresh tensions between the neighbors days after Pakistan boycotted an international conference on Afghanistan.
Pakistan asked Afghanistan to share any evidence pointing to Lashkar-e-Jhangvi, a Sunni Muslim extremist movement that was banned in 2001 by then military ruler Pervez Musharraf.
Lashkar-e-Jhangvi was one of the groups implicated in the kidnapping and beheading in 2002 of US journalist Daniel Pearl. But it has not before been tied to attacks in Afghanistan, where the Shia community has largely lived in peace even during the rule of the hardline Sunni Taliban regime.