NEW YORK — The World Trade Center’s operators apologized Monday to relatives of people killed in the 1993 bombing there, saying the country was unprepared for a terror attack that foreshadowed 9/11. The families urged people to understand its legacy.

Victims’ families, survivors, first responders and others marked the bombing’s 25th anniversary on what is now the Sept. 11 memorial plaza. They observed a silent moment, read victims’ names, laid roses on the memorial and reflected on an explosion that became a telling signal of terrorists’ aims.

“We were not ready for what visited us that day. Americans were not ready for what visited them that day,” said Kevin O’Toole, chairman of the Port Authority of New York and New Jersey, which runs the trade center. “And for that, I say: I’m sorry. And we are sorry.”

The blast in an underground parking garage on Feb. 26, 1993, killed six people, one of them pregnant. It injured more than 1,000 and forced an estimated 50,000 to flee the trade center’s twin towers in a scene of smoke, fear and confusion that would be mirrored and magnified on Sept. 11, 2001.

For families of the bombing victims, ” ’93 is as big as 9/11,” said Pat Rodriguez, who lost his pregnant sister, Monica Rodriguez Smith. “It’s a place in history that you shouldn’t forget.”

The anniversary ceremony and a memorial Mass at a nearby church have been held year after year, but the quarter-century mark brought renewed attention. It’s “long overdue” to Judy Shirtz, sister-in-law of victim Stephen Knapp. She feels the loss of families like hers has largely been forgotten amid the far greater toll of 9/11.

“It happened to us first; it shouldn’t have happened again, and it did,” she said.

Muslim extremists set off the bomb in an effort to punish the U.S. for its Middle East policies, according to federal prosecutors. The suspects weren’t directly connected to 9/11, but convicted bombing ringleader Ramzi Yousef is a nephew of self-proclaimed 9/11 mastermind Khalid Sheikh Mohammed. And another man convicted in the plot vowed that “the World Trade Center will continue to be one of our targets” in a letter later found on his laptop.

Six bombing suspects were convicted and are in prison. A seventh remains at large.

At least 100 people, including former New York Mayor David Dinkins, attended Monday’s commemoration.