The US marks the 15th anniversary of the 9/11 attacks today with solemn services to commemorate the victims of the deadliest terror strikes on US soil, which changed the world scenario. President Obama will observe a moment of silence at the White House before addressing a memorial ceremony at the Pentagon.<br/><br/>The 15th anniversary comes with the US in the midst of a divisive presidential campaign between Hillary Clinton and Manhattan tycoon Donald Trump. Both candidates are expected to attend the New York ceremony.<br/><br/>Nearly 3,000 people were killed on September 11, 2001 when 19 Al-Qaeda suicide bombers hijacked four passenger jets, crashing them into the Twin Towers in New York, the Pentagon in Washington and a field in Shanksville, Pennsylvania.<br/><br/>It was the first foreign attack on the US mainland in almost two centuries and sparked US-led invasions of Afghanistan and Iraq, where war rages on more than a decade later.