KABUL, Afghanistan - The fallout from this week's deadly suicide bombing in Kabul has further splintered Afghanistan's relations with neighboring Pakistan and set back the U.S.-led military campaign to stabilize the region before international troops leave at the end of 2014.

The attack that killed at least 60 people and wounded more than 160 outside a Shiite shrine highlighted a marked decline in security in the Afghan capital in the last year. Afghan forces, who have been in charge of security in Kabul for more than a year, have had successes in foiling plots and minimizing casualties, but insurgents increasingly slip through checkpoints and conduct assaults.

Ties between Afghanistan and Pakistan were already frayed when President Hamid Karzai on Wednesday blamed a Pakistan-based extremist group for the bombing at the shrine. Pakistan challenged Karzai to provide hard evidence.

The evidence, Karzai suggested, was that a man claiming to be from Lashkar-e-Jhangvi al-Alami, a Pakistan-based splinter group of Lashkar-e-Jhangvi that has carried out attacks against Shiite Muslims in Pakistan, called various media outlets Tuesday to claim responsibility for the Kabul bombing and a nearly simultaneous attack that killed four Shiites in the Afghan city of Mazar-e-Sharif.

"We are investigating this issue, and we are going to talk to the Pakistani government about it," Karzai said after visiting victims of the bombings.

Until now, the decade-long Afghan war has largely been spared sectarian violence, where civilians are targeted for their membership in a particular religious group. Tuesday's attack suggests some extremist groups have shifted tactics, taking aim at ethnic minorities such as the Hazara, who are largely Shiite and support the Afghan government and its Western partners.

But there was some doubt that a splinter group could carry out the coordinated bombings in Afghanistan, where neither it nor the main Lashkar-e-Jhangvi has a history of conducting operations.

Pakistani Foreign Ministry spokesman Abdul Basit said Pakistan would encourage Kabul to share any evidence it had that the group was responsible. Later, he sent a message to AP condemning the attack on the shrine. "The government and the people of Pakistan are grieved and stand by the brotherly people of Afghanistan," he said.

A Pakistani military spokesman, Gen. Athar Abbas, dismissed any suggestions that Lashkar-e-Jhangvi has links to the country's intelligence agencies or that the government was not doing everything it could to quash the group.

"Lashkar-e-Janghvi has declared war on the security forces in Pakistan," he said, noting the group has been implicated in some of the worst attacks on Pakistani security forces. "They are being hunted down."

Karzai began sharpening criticism of Pakistan after a suicide bomber, pretending to be a peace emissary from the Taliban, assassinated former President Burhanuddin Rabbani, who was leading Afghan efforts to broker a deal with the insurgency.

Afghan officials said the Sept. 20 assassination was planned on the southern outskirts of Quetta, the Pakistani city where key Taliban leaders are based. Afghan-Pakistan cooperation on the investigation into Rabbani's murder so far has been tenuous.

The recent events have left Afghanistan, Pakistan, and the United States at odds at a time when the West is trying to secure Afghanistan's future.

Pakistani Leader Hospitalized

President Asif Ali Zardari had tests related to a heart condition at a Dubai hospital Wednesday but is expected to return to Pakistan within days, officials said, denying rumors the leader may be stepping down.

Dr. Asim Hussain, a close aide, said Zardari was in the intensive-care unit not because his condition required it, "but to keep him away from frequent visitors."

"All his tests are normal, but still there are more to be carried out, which may take another 48 hours," Hussain said.

Pakistan's commissioner

to Britain, Wajid Shamsul Hasan, said Zardari, 56, had felt pain in his arm during recent meetings.

He said doctors confirmed that Zardari had a heart condition, angina.

"Whatever the case, he has no immediate plans to step down," Hasan said.

U.S. State Department spokesman Mark Toner said, "Our belief is that it's completely health-related." - Associated Press

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