Afghanistan's intelligence agency said on Saturday that it had handed Pakistan evidence that the Taliban's leadership plotted the recent assassination of ex-president and government peace envoy Burhanuddin Rabbani on Pakistani soil.
The National Directorate of Security (NDS) said that the mid-September suicide bombing that killed Rabbani, the government's top peace negotiator, was plotted in an upmarket suburb of the Pakistani city of Quetta.
The Taliban leadership council is known as the Quetta Shura, and is believed to be based in that city, although the insurgent group says it operates only from Afghanistan. Pakistan denies the existence of any Taliban shura in Quetta.
"A confession from those we detained in regard to Rabbani's assassination shows a direct involvement of the Quetta Shura," NDS spokesman Lutfullah Mashal said, adding that one of those arrested was a key player in the plot to kill Rabbani.
"(He) provided evidence and documents which we have submitted to the Pakistan Embassy. Based on mutual cooperation and diplomatic ties with Afghanistan, Pakistan is obliged to take action," he told a news conference in the Afghan capital.
Rabbani's assassination was plotted in Quetta's Satellite Town, an expensive area home to many officials and the city's elite, Mashal added.
He said a commission had been set up to investigate the killing, and further details would be given soon.
Rabbani, who became president soon after the fall of the Soviet-backed government during the early 1990s, was killed at his Kabul home by a suicide bomber claiming to be carrying a message of peace from the Taliban leadership.
Mashal said that Rabbani's killing could have been avoided if the intelligence agency had been involved in security checks on the bomber, whose name was Esmatullah, and who hid the explosives in his turban.
"We have no details of Esmatullah's identity on record with our department, he spent four days here and we were kept in darkness," he said. The agency keeps records of Taliban and former Taliban, that they could have checked him against.
"When we have been asked, we have given our full cooperation to the High Peace Council. When we cooperate we do business professionally so no one will be able to escape from our checks and can not hide things in their turbans or pockets," he said.
Rabbani was the most prominent surviving leader of the ethnic Tajik-dominated Northern Alliance of fighters and politicians and his killing has brought fears of worsening ethnic rifts among Afghans fighting the Taliban-led insurgency.
Hours after Rabbani was killed, a spokesman for the Taliban claimed responsibility for his death when talking to a Reuters reporter in Pakistan from an undisclosed location.
However, the spokesman later issued statements denying that he had made a claim of responsibility and said the Taliban were not willing to comment on Rabbani's assassination.