KABUL, Afghanistan (AP) -- An Afghan government commission investigating the assassination of former President Burhanuddin Rabbani accused Pakistan on Tuesday of refusing to cooperate with the probe after allegations that Pakistani intelligence officials had advance knowledge of the plot.
If Pakistan does not help, Afghanistan will appeal to the United Nations to get involved, said the commission spokesman and deputy chief of the Afghan intelligence service, who goes by the single name of Dr. Zia.
Afghanistan and Pakistan have long been uneasy allies against the Taliban insurgency, and relations have become increasingly strained since the death of Rabbani, who was appointed by the government to try to broker peace with the Taliban. A host of Afghan officials have publicly accused Pakistan and its spy agency of supporting the militants behind the slaying.
Pakistan's government said it was cooperating and denied involvement in the Sept. 20 killing.
"Prime Minister (Reza Yousuf) Gilani had offered cooperation in the investigation into professor Rabbani's assassination during his visit to Kabul," said Pakistani Foreign Ministry spokeswoman Tehmina Janjua. "Pakistan stands by this commitment."
The assassin gained entry to Rabbani's home by claiming to be a peace emissary from the Taliban's governing council, which is based in Pakistan. As he neared Rabbani he detonated explosives that were hidden inside his turban.
Speaking to reporters, Zia said the sophistication of the bomb pointed to a link with Pakistan.
He said the commission was also basing its accusations of Pakistani involvement on the confession of the suspected mastermind, Hamidullah Akundzadeh, an Afghan who was arrested 18 hours after Rabbani was assassinated.
The intelligence service says the bomber was a Pakistani man named Esmatullah.
"Why are we claiming Pakistan government is behind this attack? Because the explosive that was in that hat was not the idea of a few Taliban leaders," Zia said. "It was a very sophisticated device inside that hat."
He said that just one hour before his news conference the Pakistani government delivered a message through its embassy informing "us that they are not ready to cooperate with us."
He added that their explanation suggested Pakistan was upset with remarks about the case that Afghan officials had made to the media.
"Now we have to go to the U.N. for help," he said.
Zia stopped short of directly accusing Pakistani intelligence authorities of being behind the explosive device, but Afghan Interior Minister Bismullah Khan Mohammadi said Oct. 1 in an Afghan parliamentary session that the ISI was involved in the killing.
Zia said that according to Akundzadeh's confession, the plan to assassinate Rabbani was hatched six months ago and that he was targeted for being both a high-ranking official and the head of the peace council.
He alleged that the Pakistani agency knew about the attack, which he said also had the involvement of the Quetta Shura, the ruling council of the Taliban that is based in the southern Pakistani city of the same name.
"They have the full support of the Pakistan government," he said.
Pakistan denied the allegation last Sunday, calling it "baseless." It said the evidence given to Pakistan consisted solely of the confession of Akundzadeh.
"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 toward peace and toward Pakistan are systematically being removed from the scene and killed," said Pakistan's Foreign Ministry in a written statement issued on Sunday.
Karzai has not openly blamed Pakistan for the killing, but has said they have not done enough for peace.
"Regretfully, the Islamic Republic of Pakistan did not cooperate with Afghanistan to bring peace and security. We hope is that Pakistan government understands it's in people's interest to assist both countries in bringing peace and stability," Karzai said in a nationally televised address on Monday.