A firefighter pauses for a quiet moment as friends and relatives of the victims of 9/11 gather for a ceremony marking the 12th anniversary of the attacks at the National September 11 Memorial at the World Trade Center site, Wednesday, Sept. 11, 2013, in New York. (AP Photo/Jason DeCrow)

NEW YORK, N.Y. - Sept. 11 victims' loved ones will gather at ground zero to commemorate the anniversary of the terrorist attacks with the reading of names, moments of silence and serene music that have become tradition.

At Wednesday's ceremony on the 2-year-old memorial plaza, relatives will recite the names of the nearly 3,000 people who died when hijacked jets crashed into the World Trade Center and the Pentagon and near Shanksville, Pennsylvania, as well as the names of victims of the 1993 trade centre bombing. Beforehand, Gov. Andrew Cuomo, musician Billy Joel, firefighters and others are expected to join in a tribute motorcycle ride from a Manhattan firehouse to ground zero.

Name-reading, wreath-laying and other tributes also will be underway at the Pentagon and at the Flight 93 National Memorial in Shanksville while the commemoration unfolds at ground zero, where the mayor who has helped orchestrate the observances from their start will be watching for his last time in office. And saying nothing.

Continuing a decision made last year, no politicians will speak, including Mayor Michael Bloomberg.

Over his years as mayor and chairman of the National Sept. 11 Memorial & Museum, Bloomberg has sometimes tangled with victims' relatives, religious leaders and other elected officials over an event steeped in symbolism and emotion. But his administration has largely succeeded at its goal of keeping the commemoration centred on the attacks' victims and their families and relatively free of political image-making.

Memorial organizers expect to take primary responsibility for the ceremony next year and say they plan to continue concentrating the event on victims' loved ones, even as the forthcoming museum creates a new, broader framework for remembering 9-11.

"As things evolve in the future, the focus on the remembrance is going to stay sacrosanct," memorial President Joe Daniels says.

Wednesday's anniversary also arrives with changes coming at the Flight 93 National Memorial in Shanksville, where officials gathered Tuesday to herald the start of construction on a visitor centre. At the Pentagon, plans call for a morning ceremony for victims' relatives and survivors of the attacks and an afternoon observance for Pentagon workers.

President Barack Obama will join first lady Michelle Obama, Vice-President Joe Biden, Jill Biden and members of the White House staff in a moment of silence on the White House South Lawn. The president will then attend the Sept. 11 observance at the Pentagon.

Around the world, thousands of volunteers have pledged to do good deeds, honouring an anniversary that was designated a National Day of Service and Remembrance in 2009. Obama will take part in a service project on Wednesday afternoon.

When Bloomberg and then-Gov. George Pataki announced the plans for the first anniversary in 2002, the mayor said the "intent is to have a day of observances that are simple and powerful."

His role hasn't always been comfortable. When the ceremony was shifted to nearby Zuccotti Park in 2007 because of rebuilding at the trade centre site, some victims' relatives threatened to boycott the occasion. The lead-up to the 10th anniversary brought pressure to invite more political figures and to include clergy in the ceremony.

By next year's anniversary, Bloomberg will be out of office, and the museum is expected to be open beneath the memorial plaza.

While the memorial honours those killed, the museum is intended to present a broader picture of 9-11, including the experiences of survivors and first responders.

But the organizers expect they "will always keep the focus on the families on the anniversary," Daniels said.

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News from © The Associated Press, 2013