Bells toll as US marks 22 years since horror of September 11

First responders salute as an American flag is unfurled at the Pentagon at sunrise to commemorate the 2001 terrorist attack on the Pentagon, during an observance ceremony in Washington, DC (AP)

Bells have tolled at ground zero and solemn tributes were paid around the US as Americans looked back on the horror and legacy of the September 11 terror attacks.

People gathered at memorials, fire stations, city halls, campuses and elsewhere to observe the 22nd anniversary of the deadliest terror attack on US soil on September 11 2001.