Story highlights Human Rights Watch says deal compounds "culture of impunity"

Gulbuddin Hekmatyar had a ruthless reputation

Kabul, Afghanistan (CNN) After months of delays, Afghan government negotiators signed a peace deal Thursday with an insurgent faction led by one of the country's most notorious warlords.

The deal was signed at a ceremony attended by negotiators, the President's national security adviser, and representatives of the Hezb-i-Islami faction of Gulbuddin Hekmatyar.

Afghan and US officials applauded the agreement, but a prominent human rights organization strongly criticized the deal.

In a statement, the US Embassy called Thursday's accord "a step in bringing the conflict in Afghanistan to a peaceful end."

That sentiment was echoed by Afghanistan's chief executive -- who is in a shaky power-sharing agreement with the country's President.

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