Former Afghan President Berhanuddin Rabbani was killed in an attack at his home on September 20.

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Berhanuddin Rabbani was spearheading peace efforts with the Taliban

One person has been arrested, an intelligence official says

"We cannot deny the involvement of Quetta Shura," he says

Kabul, Afghanistan CNN  — 

The assassination of Berhanuddin Rabbani, an Afghan leader spearheading the reconciliation process with the Taliban, was planned outside the country, an Afghan intelligence official said Monday.

Rabbani, a former Afghan president and chairman of the High Peace Council, was killed in an attack at his home on September 20.

“We have arrested one individual who is a citizen of Afghanistan,” the official, who declined to be named, told reporters at a news conference. “But who these people are or who the organization involved in the attack is, we will say that in the future.”

“We cannot deny the involvement of Quetta Shura,” he said. Quetta Shura is a leadership council based in the Pakistani city of Quetta, thought to run much of the Taliban insurgency in Afghanistan.

No one in the Afghan government played a role in Rabbani’s death, he said. “This was a terrorist act and was planned very carefully outside Afghanistan.”

Rabbani’s death shocked the war-torn country, undermined the fledgling peace initiative and stoked fears of renewed ethnic conflict between Pashtuns and others, such as Rabbani’s ethnic group of Tajiks.

An Afghan intelligence source told CNN last week that the bomber arrived at the house at the same time a meeting was due to take place between Rabbani and a delegation representing the Taliban insurgency.

Police said the bomber claimed to be a Taliban member who had come for the talks about peace and reconciliation and detonated the explosives as he entered the home.

Long an enemy of the Taliban, Rabbani was a controversial choice when appointed by President Hamid Karzai as chairman of the High Peace Council a year ago. He was forced to flee Kabul when the Taliban took over in 1996, but he continued to lead resistance to the regime from his stronghold in Faizabad in northern Afghanistan.

Journalist Ruhullah Khapalwak contributed to this report.