WASHINGTON, Aug 18 (Reuters) - U.S. Defense Secretary Lloyd Austin said on Wednesday there were about 4,500 U.S. military personnel in Afghanistan"s capital Kabul and there "have been no hostile interactions with the Taliban and our lines of communication with Taliban commanders remain open." Reporting by Idrees Ali, Patricia Zengerle, David Brunnstrom, writing by Michelle Nichols, Editing by Franklin Paul Our Standards: The Thomson Reuters Trust Principles.