I am not sure if the sentence is written this way purposely, but it says that talking to Taliban has been impeded by something that is actually missing? Or maybe 'impeded by' has some other meaning in this context?
Talking to the Taliban has always been impeded by the lack of a brass plate on an office door somewhere announcing their presence.
It is OK. A missing thing can also impede you. My lack of a driver's license impeded my opportunity travel.
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