Hillary Clinton's unsecured home server contained more than a dozen emails deemed "top secret"- one of the highest levels of classification in the US government, the White House has said.<br />State Department spokesman John Kirby said the documents were not marked classified at the time they were sent.<br />Mrs Clinton's use of a personal email as secretary of state has become an issue in her presidential campaign.<br />This is the first time her emails have been labelled classified at any level.<br />Messages were marked "top secret" because they would cause "exceptionally grave" damage to national security if disclosed, the State Department said.
