Afghan President Hamid Karzai has joined mourners at the funeral of former preisdent Burhanuddin Rabbani, who was killed by a suicide bomber claiming to carry a message of peace from the Taliban.

Mr. Karzai said it is “our responsibility” to act against those who are “enemies of peace” as he paid tribute to Mr. Rabbani at the presidential palace in Kabul.

A suicide bomber killed Mr. Rabbani Tuesday in the capital. The former president was the head of Afghanistan's High Peace Council and was spearheading peace efforts with the Taliban.

Police say the ex-president was killed in his home by an assassin who had a bomb hidden under his turban.

Kabul is under tight security for the funeral services.

President Karzai said Thursday the suicide bomber had presented officials with an audio message of a purported Taliban peace offer and that he had listened to it before leaving for New York to attend the United Nations General Assembly. Mr. Karzai cut short his U.S. trip after Mr. Rabbani's assassination.

President Karzai said his advisor, Masoom Stanekzai, who was wounded in the attack, gave him the audio message. Officials say Mr. Rabbani rushed home from a trip to Iran to meet the purported Taliban emissary.

Pakistani Prime Minister Yousuf Raza Gilani traveled to Kabul Thursday to offer his condolences.

A spokesman for the Afghan intelligence agency said Thursday officials believe the Taliban's leadership body — the Quetta Shura — was behind the assassination.

There is conflicting information regarding the claim of responsibility. A Taliban spokesman told the Reuters news agency that the group carried out the attack, but another Taliban spokesman rejected that claim and said the insurgent group would not comment on Mr. Rabbani's assassination.