By Parisa Hafezi and Steve Holland DUBAI/WASHINGTON, July 12 (Reuters) - Iran on Sunday said it closed the Strait of Hormuz after a vessel traveled on an unapproved route and was struck, warning that any retaliation over the incident would be met with a "severe response." "A vessel that had jeopardized maritime security by switching off its systems was struck and brought to a halt," the Navy of Iran's Islamic Revolutionary Guard Corps said in a statement, without giving any details about the…