Police have blown up two backpacks found near the Boston Marathon's finish line and have arrested and charged a man in connection with the find.
A man taken into custody near the scene had a rice cooker in his backpack and is being charged with possession of a hoax device, disturbing the peace and disorderly conduct, officers said.
The man was stopped by an officer who saw him acting suspiciously. He says the man dropped the backpack and it was later blown up by the bomb squad as a precaution, as was a second unattended backpack found nearby.
Detectives could not confirm what was in the second backpack or who owned it.
The backpacks rattled nerves on the anniversary of the Boston Marathon bombing, in which two pressure cooker bombs in backpacks killed three people.
Survivors, first responders and family members of those killed came together earlier to mark the anniversary of the bombing with solemn ceremonies.
Former mayor Thomas Menino addressed an invitation-only audience of about 2,500 people at the Hynes Convention Centre, not far from the finish line where more than 260 others were killed or wounded a year ago.
"This day will always be hard, but this place will always be strong," he said.
In Washington, president Barack Obama said: "Today, we recognise the incredible courage and leadership of so many Bostonians in the wake of unspeakable tragedy. And we offer our deepest gratitude to the courageous firefighters, police officers, medical professionals, runners and spectators who, in an instant, displayed the spirit Boston was built on - perseverance, freedom and love."
Mr Obama said this year's race would "show the world the meaning of Boston Strong as a city chooses to run again".
Vice president Joe Biden was in Boston for the ceremony, and he said the courage shown by survivors and those who lost loved ones was an inspiration for other Americans dealing with loss and tragedy.
"We are Boston. We are America. We respond. We endure. We overcome. And we own the finish line," he concluded, to loud applause.
Earlier in the day, a wreath-laying ceremony drew the families of the three people killed - Martin Richard, Krystle Campbell and Lu Lingzi - as well as relatives of Massachusetts Institute of Technology police Officer Sean Collier, who was killed in the aftermath of the blasts.
Governor Deval Patrick, mayor Martin J Walsh and Boston Cardinal Sean O'Malley were among those who attended the morning ceremony held in a light rain as bagpipes played. Cardinal O'Malley offered a prayer.
The victims were also honored at the Hynes centre, where the survivors who spoke included newlywed Patrick Downes and dancer Adrianne Haslet-Davis, both of whom lost their lower left legs in the bombings.
At 2.49pm, a moment of silence was held at the finish line to mark the time and place where two bombs exploded last April 15. It was followed by a flag-raising by officer Richard Donohue, who was badly wounded in a shootout with the bombing suspects.
Authorities say two brothers planned and orchestrated the attack and later shot and killed Mr Collier during an attempt to steal his gun. Tamerlan Tsarnaev, 26, died following a shootout with police days after the bombings. Dzhokhar Tsarnaev, 20, has pleaded not guilty to 30 federal charges and is awaiting trial. He faces the possibility of the death penalty.