The United States on Sunday marked the 15th anniversary of the 9/11 attacks with solemn services all over the country. President Barack Obama will address a ceremony at the Pentagon, and the names of those who lost their lives will be read out in a remembrance service. The National September 11 Memorial and Museum in New York City will host its first art exhibition, called 'Rendering the Unthinkable: Artists Respond to 9/11'. It will showcase works by 13 artists who have been affected by the attacks.

More than 3,000 people died when two hijacked planes crashed into the World Trade Centre on this day 15 years ago. Terror group al-Qaeda orchestrated the attacks, which also involved two other hijacked aircraft that were targeted at the Pentagon and Washington DC.

The second tower of the World Trade Center bursts into flames after being hit by a hijacked airplane in New York on September 11, 2001. File photo. Reuters.
Visitors walk among US flags erected to pay tribute to 9/11 victims at Pepperdine University. AFP photo
Students place 3,000 flags across the university's Malibu campus in California. AFP photo
Members of the New York Police Department's Emerald Society Pipe & Drum Band hold a moment of silence. Reuters photo
Bikers take part in the America's 911 Ride 'The Final Ride' in New York on August 21. AFP photo