"We have eyewitness accounts of Taliban's widespread atrocities perpetuated with support of foreign terrorist fighters and foreign intelligence and military assets," Isaczai said during a UN Security Council meeting on Thursday.
"They have performed targeted executions, cutoff communication lines, and imposed a humanitarian blockade", he added.
Isaczai called on the UNSC not to recognize any government in Kabul unless it is genuinely inclusive.
"I… ask you to withhold any recognition of any government in Afghanistan, unless it's truly inclusive and formed on the basis of the free will of the people," Isaczai said.
The envoy said the UN Security Council should also reevaluate its approach to granting travel ban exemption to Taliban leaders who are sanctioned after they failed to resolve the conflict through peaceful means.
"Al-Qaeda* members remain in Afghanistan, visibly welcomed and sheltered by the de-facto Taliban authorities. Islamic State*-Khorasan Province remains active and could gain strength."
The Taliban, which seized power in Afghanistan on August 15, unveiled the composition of an interim government which, contrary to international calls and expectations, is not inclusive of non-Taliban members and women.
*Terrorist organizations banned in Russia and many other states