The comments by Gulbuddin Hekmatyar came after the armed wing of his Hezb-i-Islami party effectively scuttled the deal, drafted weeks ago, with new demands. Hekmatyar called Afghanistan's government illegal and said he would not recognise it.
In his lengthy diatribe against the Kabul government in the Daily Shahdat magazine belonging to his group, Hekmatyar said the Afghan administration negotiated in bad faith and made demands it could not meet.
Afghan President Ashraf Ghani's government had hoped an agreement with Hekmatyar would be an incentive for other insurgent groups to come to the negotiating table.
Hekmatyar, writing under his pen name Haqpal, said Afghan government negotiators called the security pact with the United States "a red line that we cannot cross."
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Hekmatyar said only a handful of his group's demands were met in the draft agreement, yet last month when his representatives left Kabul they said they had a final deal that needed only Hekmatyar's signature. Instead Hekmatyar returned the agreement with the additional demands.
Hekmatyar's military strength pales in comparison to the Taliban and is largely limited to the east and northeast of the country. Hekmatyar also has differences with the Taliban and his fighters have clashed with them on several occasions in eastern Afghanistan.