US President Barack Obama has paid tribute to the "resilience" of the American people ahead of the 15th anniversary of the September 11 attacks.

In a video released on 10 September, Obama said the "core values" that defined the US had not changed despite the devastating attacks that killed nearly 3,000 people and injured more than 6,000 others.

He said the threat of terrorism had "evolved" over the past decade and that the US will continue to pursue groups such as al-Qaeda and Islamic State (Isis).

"As we reflect on these past 15 years, it's also important to remember what has not changed – the core values that define us as Americans; the resilience that sustains us," the president stated.

"After all, terrorists will never be able to defeat the United States. Their only hope is to terrorise us into changing who we are or our way of life.

"That's why we Americans will never give in to fear. And it's why this weekend we remember the true spirit of 9/11."

Despite the emergence of fresh threats such as IS (Daesh), Obama urged Americans to not react in ways that "erode the fabric of our society".

"In the face of terrorism, how we respond matters. We cannot give in to those who would divide us," he said.

US President Barack Obama has paid tribute to the 'resilience' of Americans Getty

"Because it's our diversity, our welcoming of all talent, our treating of everybody fairly – no matter their race, gender, ethnicity or faith – that's part of what makes our country great. It's what makes us resilient.

"And if we stay true to those values, we'll uphold the legacy of those we've lost and keep our nation strong and free."

The September 11 attacks – carried out by 19 al-Qaeda militants who hijacked four passenger planes and crashed them into the Twin Towers in New York, the Pentagon in Washington, and a field in Pennsylvania – were the first foreign attacks on the US mainland in almost 200 years.

A ceremony will be held at Ground Zero in New York to commemorate the victims of the attack, while Obama will speak at a ceremony at the Pentagon.