Hailing the values and resilience that he says both define and sustains Americans, President Barack Obama on Saturday honored the nearly 3,000 people who were killed in the terrorist attacks of 11 September 2001, as well as the bravery of survivors and the emergency personnel who responded, and the work of scores of others who have labored since to keep the US safe.

In his weekly address, Obama said that while so much has changed in the years since 9/11 it is important to remember what has stayed the same.

“The core values that define us as Americans. The resilience that sustains us,” he said, on the eve of the 15th anniversary of one of the nation’s darkest days.

Obama said terrorists want to frighten Americans into changing how they live, but “Americans will never give in to fear”.

“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,” Obama said.

Nearly 3,000 people were killed in New York City, Pennsylvania and at the Pentagon when hijacked commercial airliners crashed in attacks that were planned and carried out by the al-Qaida terrorist group. Al-Qaida leader Osama bin Laden was killed nearly a decade later by US forces during a May 2011 raid on his Pakistani hideout that Obama authorized.

Obama noted in his address that the terrorist threat has evolved “as we’ve seen so tragically from Boston to Chattanooga, from San Bernardino to Orlando,” cities that suffered headline-grabbing and terrorist-linked attacks.

He pledged that the US would stay relentless against terrorism from al-Qaida and the Islamic State group, which is spreading across the Middle East and the west.

Obama will mark Sunday’s anniversary of 9/11 by observing a moment of silence in the privacy of the White House residence at 8.46am ET, when American Airlines Flight 11 crashed into the north tower of the World Trade Center. He will then deliver remarks at a Pentagon memorial service.

The state department, meanwhile, was reminding US citizens about threats around the world and urging Americans to be vigilant about personal security.

The department’s latest worldwide caution said “current information suggests that terrorist groups continue to plan attacks in multiple regions” and that extremists “may use conventional or nonconventional weapons to target official government and private interests”.

The US government says extremists remain interested in “soft targets” such as high-profile public events; hotels, clubs and restaurants; places of worship; schools; shopping malls and markets; public transportation systems; and events where Westerners gather in large numbers, including during holidays.

The department notes that US government facilities worldwide remain at a “heightened state of alert”.