DUBAI, Sept 7 (Reuters) - U.S. Secretary of State Anthony Blinken said on Tuesday Washington has identified a "relatively" small number of Americans seeking to depart from Afghanistan"s Mazar-i-Sharif. Blinken, who was speaking with his Qatari counterpart in a joint press conference in Doha, said that the challenge with the evacuation charter flights is that some Afghans seeking to leave do not have appropriate documents.