US President Barack Obama mourned those killed in the Sept. 11 attacks on the 15th anniversary and, in his weekly radio address, reassured the nation "we are still an America of heroes who ran into harm's way."

Obama said "much has changed" in the ongoing pursuit of global extremist groups, noting progress fighting the Daesh and al-Qaeda. Still, he said Americans must remain vigilant in the wake of Daesh-inspired attacks on US soil.

"A lot has changed over these past 15 years. We've delivered devastating blows to the al-Qaeda leaders that attacked us on 9/11," Obama said. "We delivered justice to Osama bin Laden. We've strengthened our homeland security. We've prevented attacks. We've saved lives.

"At the same time, the terrorist threat has evolved, as we've seen so tragically from Boston to Chattanooga, from San Bernardino to Orlando. So in Afghanistan, Iraq, Syria and beyond, we'll stay relentless against terrorists like al-Qaida and [the Islamic State]. We will destroy them. And we'll keep doing everything in our power to protect our homeland."

Obama, quoting Scripture, encouraged Americans to reflect on the legacy of the Sept. 11 attacks and how millions responded with an outpouring of love and a greater sense of community.

"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. After all, terrorists will never be able to defeat the United States. Their only hope is to terrorize 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. We're still the America of heroes who ran into harm's way; of ordinary folks who took down the hijackers; of families who turned their pain into hope. We are still the America that looks out for one another, bound by our shared belief that I am my brother's keeper, I am my sister's keeper.

Earlier this week, the US increased its deployment by 500 troops to fight against Daesh in Mosul, which the US-led coalition and Iraqi security forces hope to retake by the end of the year.

By Eric DuVall

Editor's note: This article has been edited from the source material.