Nearly a quarter century has passed since the Sept. 11, 2001, attacks, but for many, the emotions of the day remain raw as ever.

On Thursday, America marked the 24th anniversary of the deadly attacks with solemn ceremonies in New York, at the Pentagon and in Shanksville, Pennsylvania.

The commemorations were punctuated by moments of silence, the tolling of bells and the reading of the names of the nearly 3,000 killed.

In a rural field near Shanksville, Pennsylvania, a ceremony attended by Veterans Affairs Secretary Doug Collins honored the victims of Flight 93, the hijacked plane that crashed after crew members and passengers tried to storm the cockpit.

"We honor their actions as a truly heroic display of unity, courage, and defiance in the face of tremendous adversity," National Park Service and Flight 93 National Memorial Superintendent Stephen Clark told those attending the ceremony.

"We must always remember what happened 24 years ago today, when an attack on our nation brought forth an inspiring show of courage from the passengers and crew members aboard Flight 93," Clark said.

Robert J. Way is a pastor for the Good Shepherd Cooperative Lutheran Ministries in Shanksville.

He honored the victims by leading moments of silence and providing solace to family members who lost loved ones that day.

"What was once a common field is now a field of honor. It is our privilege to continue moving forward to preserve and nurture this hallowed place. Hallowed not by us, but by the lives of your loved ones."

Elsewhere, people marked the anniversary with service projects and charitable works as part of a national day of service.

Volunteers took part in food and clothing drives, park and neighborhood cleanups, blood banks and other community events.

In all, the attacks by al-Qaida militants killed 2,977 people, including many financial workers at the World Trade Center and firefighters and police officers who had rushed to the burning buildings trying to save lives.

The attacks reverberated globally, altering the course of U.S. foreign and domestic policy.

It led to the “Global War on Terrorism” and the U.S.-led invasions of Afghanistan and Iraq and related conflicts that killed hundreds of thousands of civilians and troops.

The U.S. government has also spent billions of dollars providing health care and compensation to tens of thousands of people who were exposed to the toxic dust that billowed over parts of Manhattan when the twin towers collapsed.

While the hijackers died in the attacks, federal officials have struggled to conclude the long-running legal case against the man accused of masterminding the plot, Khalid Sheikh Mohammed.

The former al-Qaida leader was arrested in 2003, but has never received a trial.

The Trump administration has also acknowledged its considering ways to take control of the ground zero memorial plaza and its underground museum, which are run by a public charity.