US President Barack Obama is due to visit Boston to honour the victims of the deadly marathon bombings, after a suspect was apparently caught on CCTV planting a device.
The president will attend an interfaith service at the city's Cathedral of the Holy Cross, three days after the devastating blasts claimed three lives and injured dozens more.
Nobody has claimed responsibility for the twin explosions which killed eight-year-old Martin Richard, Krystle Campbell, 29, and a Chinese graduate student, named in reports as Lu Lingzi.
There was confusion on Wednesday night after several media outlets reported that a suspect was in custody and was due to appear in court over the atrocity, but investigators later urged caution over the reports and insisted no one had been arrested.
An FBI statement read: "Contrary to widespread reporting, there have been no arrests made in connection with the Boston Marathon attack. Over the past day and a half, there have been a number of press reports based on information from unofficial sources that has been inaccurate.
"Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting."
Meanwhile, it has been reported that a suspect was identified from surveillance video taken at a Lord & Taylor department store between the sites of the two bomb blasts.
Mr Obama's visit to Boston comes after it emerged he was sent a letter apparently containing poisonous ricin. There was no indication the letter, which was intercepted by the White House, was connected to the marathon bombings, the FBI said.
Mr Obama has called the marathon bombings an act of terrorism. Speaking at a press conference, he said: "This was a heinous and cowardly act. The FBI is now investigating this as an act of terrorism."
He added: "The American people refused to be terrorised. What the world saw yesterday in the aftermath of the explosions were stories of heroism and kindness and generosity and love."