KABUL—Russia is hindering the removal of one of Afghanistan’s most notorious warlords from a United Nations sanctions list, Afghan and Western officials said Monday, a move that could complicate efforts to implement a peace deal seen as a model for a similar accords with the Taliban and other insurgent groups.

The U.S. and the North Atlantic Treaty Organization hailed the agreement reached in September between the Afghan government and Hezb-e Islami, an Islamist political and militant group led by Gulbuddin Hekmatyar as a hopeful sign in efforts to end bloodshed in Afghanistan.

Under terms of the deal, the Afghan government asked the U.N. in December to take Mr. Hekmatyar off its list of those subject to international sanctions for ties to al Qaeda.

During the 10-day period for member states to respond, Russia said it needed more time to consider the request. According to U.N. rules, it has up to six months to provide reasoning for its opposition.

Russian Foreign Ministry spokeswoman Maria Zakharova said on Monday that Moscow had put the delisting on hold but hadn’t blocked it. She didn’t explain why Russia needed more time to consider the move.