(CNN) -- Afghan officials stepped up accusations Sunday that the assassination of the country's peace council chairman began with a plot in Pakistan and was carried out by a citizen of the neighboring nation.
Afghanistan's interior minister said Sunday that Pakistan's Inter-Services Intelligence agency also played a role in the attack, which he said came after months of planning by a Taliban group based in Pakistan.
"There are no doubts that ISI had its involvement in the plot," Interior Minister Bismillah Mohammadi told Afghan lawmakers. "We have handed over the documents and proof to the Pakistani government."
Pakistan's foreign ministry denied the claims, decrying them as "baseless allegations."
"Instead of making such irresponsible statements, those in positions of authority in Kabul should seriously deliberate as to why all those Afghans who are favorably disposed towards peace and towards Pakistan are systematically being removed from the scene and killed," Pakistan's Ministry of Foreign Affairs said in a statement.
Burhanuddin Rabbani, who was spearheading the reconciliation process with the Taliban in Afghanistan, was killed in a September 20 suicide bombing at his home.
Earlier Sunday, an Afghan commission said the plot to kill Rabbani began in Quetta, Pakistan, according to an Afghan government statement summarizing a report the investigatory group presented. The commission also said the suicide attacker who killed Rabbani was a Pakistani citizen, citing documents and an accused accomplice's confession as evidence.
"The commission members prove that the documents they have received together with names addresses and phone numbers people involved in this case have been handed over to the government of Pakistan," the statement said.
Pakistan's foreign ministry said the embassy had received a copy of a "confessional statement" from an Afghan national accused of masterminding the assassination. The ministry accused Afghan officials of holding back some details from the confession.
"The Afghan interior minister has not highlighted the fact that the assassin and his handler were roaming around in Kandahar and Kabul for quite some time," the Pakistani ministry's statement said.
The confession also says that before the killing, the suicide attacker stayed in a guest house managed by Afghans close to Rabbani, according to Pakistan's foreign ministry.
Police earlier said the suicide 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.
On Saturday, Afghanistan's intelligence service said it provided evidence -- including photographs, documents and maps -- to Pakistan's embassy in Afghanistan, showing that the assassination of Rabbani was planned by the Taliban council in Quetta.
Rabbani was a former Afghan president who was considered vital to peace efforts in the country.
His 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.
Pakistan's foreign ministry said it "unequivocally condemned the act of terrorism that led to" Rabbani's death, saying he was "a great friend of Pakistan and widely respected" there.
Sunday's accusations from Afghan officials came a day after Afghan President Hamid Karzai dismissed calls for negotiations with the Taliban, saying Pakistan is the key to peace talks with the insurgency.
CNN's Reza Sayah, Nick Paton Walsh and journalist Ruhullah Khapalwak contributed to this report.