A statement by NDS said the suicide bomber has been identified as Shah Ghulam who was recruited by Sirajuddin Haqqani and was sent to Khost city with the help of Mawlavi Abdul Rahman.
The statement further added that the bomber detonated his explosives among the rally participants after receiving instructions from Haqqani network leader.
NDS said the suspects involved in the attack have been identified and vowed to take immediate actions to eliminate or arrest the perpetrators.
At least 20 people were killed and over 60 others were injured in the attack.
The Haqqani terrorist network is accused of staging numerous cross-border attacks from their base in North Waziristan, including the 19-hour siege at the US Embassy in Kabul in Septemebr 2011.
Haqqani network was formed in the late 1970s by Jalaluddin Haqqani. The group is allied with al-Qaida and the Afghan Taliban and cooperates with other terrorist organizations in the region.
The netework is considered the most lethal insurgent group targeting the NATO-led coalition security forces and Afghan personnel in Afghanistan.
The US Departmnt of State designated the HQN as a Foreign Terrorist Organization on September 7, 2012.